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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

ELVES-Dwarf. I. Satellite Systems of Eight Isolated Dwarf Galaxies in the Local Volume

The satellite populations of Milky Way (MW)–mass systems have been extensively studied, significantly advancing our understanding of galaxy formation and dark matter physics. In contrast, the satellites of lower-mass dwarf galaxies remain largely unexplored, despite hierarchical structure formation predicting that dwarf galaxies should host their own satellites. We present the first results of the ELVES-Dwarf survey, which aims to statistically characterize the satellite populations of isolated dwarf galaxies in the Local Volume (4 < D < 10 Mpc). We identify satellite candidates in integrated light using Legacy Surveys data and achieve completeness down to M g ≈ −9 mag. We then confirm the association of satellite candidates with host galaxies using surface-brightness fluctuation distances measured from Hyper Suprime-Cam data. We surveyed eight isolated dwarf galaxies with stellar masses ranging from sub-Small Magellanic Cloud to Large Magellanic Cloud scales $(10^{7.8} < M^{\textrm{host}}_{\star} < 10^{9.5} M_⊙)$, and confirmed six satellites with stellar masses between 10 5.6 and 10 8 M ⊙ . Most confirmed satellites are star-forming, in contrast to the primarily quiescent satellites observed around MW-mass hosts. By comparing observed satellite abundances and stellar mass functions with theoretical predictions, we find no evidence of a “missing satellite problem” in the dwarf galaxy regime.

Li, Jiaxuan 嘉轩李 [Princeton University, NJ (United ↗
DOE OSTI2022

Dynamics of stellar disc tilting from satellite mergers

The Milky Way’s stellar disc can tilt in response to torques that result from infalling satellite galaxies and their associated tidal debris. In this work, we explore the dynamics of disc tilting by running N-body simulations of mergers in an isolated, isotropic Milky Way-like host galaxy, varying over satellite virial mass, initial position, and orbit. We develop and validate a first-principles understanding of the dynamics that govern how the host galaxy’s stellar disc responds to the satellite’s dark matter (DM) debris. We find that the degree of disc tilting can be large for cosmologically motivated merger histories. In particular, our results suggest that the Galactic disc may still be tilting in response to Gaia-Sausage-Enceladus, one of the most significant recent mergers in the Milky Way’s history. In conclusion, these findings have implications for terrestrial direct detection experiments as disc tilting changes the relative location of the Sun with respect to DM substructure left behind by a merging galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Space Interferometry Mission: Dynamical Observations of Galaxies (SIMDOG)

Space Interferometry Mission (SIM) will be used to obtain proper motions for a sample of 27 galaxies; the first proper motion measurements of galaxies beyond the satellite system of the Milky Way. SIM measurements lead to knowledge of the full 6-dimensional position and velocity vector of each galaxy. In conjunction with new gravitational flow models, the result will be the first total mass measurements of individual galaxies. The project, includes developnient of powerful theoretical methods for orbital calculations. This SIM study will lead to vastly improved determinations of individual galaxy masses, halo sizes, and the fractional contribution of dark matter. Astronomers have struggled to calculate the orbits of galaxies with only position and redshift information. Traditional N-body techniques are unsuitable for an analysis backward in time from a present distribution if any components of velocity or position are not very precisely known.

Shaya, Edward J.↗
DOE OSTI2020

The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

The Sloan Digital Sky Surveys (SDSS) have been observing the skies from Apache Point Observatory (APO) since 1998 (using the 2.5m Sloan Foundation Telescope, Gunn et al. 2006) and from Las Campanas Observatory (LCO) since 2017 (using the du Pont 2.5m Telescope). Representing the fourth phase of SDSS, SDSS-IV (Blanton et al. 2017) consists of three main surveys; the Extended Baryon Oscillation Spectroscopic Survey (eBOSS; Dawson et al. 2016), Mapping Nearby Galaxies at APO (MaNGA; Bundy et al. 2015), and the APO Galactic Evolution Experiment 2 (APOGEE-2; Majewski et al. 2017). Within eBOSS, SDSS-IV has also conducted two smaller programs: the SPectroscopic IDentification of ERosita Sources (SPIDERS; Clerc et al. 2016; Dwelly et al. 2017) and the Time Domain Spectroscopic Survey (TDSS; Morganson et al. 2015). These programs have investigated a broad range of cosmological scales, including cosmology with large-scale structure in eBOSS, the population of quasars and variable or X-ray-emitting stars with TDSS and SPIDERS; nearby galaxies in MaNGA; and the Milky Way and its stars in APOGEE-2.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Self-interacting Dark Matter Interpretation of Crater II

Abstract The satellite galaxy Crater II of the Milky Way is extremely cold and exceptionally diffuse. These unusual properties are challenging to understand in the standard model of cold dark matter. We use controlled N -body simulations to investigate the formation of Crater II in self-interacting dark matter (SIDM), where dark matter particles can scatter and thermalize. Taking the orbit motivated by the measurements from Gaia Early Data Release 3, we show a strong self-interacting cross section per particle mass of 60 cm 2 g −1 is favored for Crater II. The simulated SIDM halo, with a 1 kpc core, leads to both a low stellar velocity dispersion and a large half-light radius for Crater II. These characteristics remain robust regardless of the initial stellar distribution.

Astronomy & Astrophysics↗
NASA NTRS1972

New horizons in astronomy.

Besides the study of astronomy itself, other topics included cover the geological and biological developments on earth and basic physics of matter, heat, and light. Optical and radio telescopes are discussed, as well as photographic and photoelectric means of detection. The immediate solar system is described by topics on the properties and atmospheres of the inner and outer planets, the sun's energy, sunspots, and the solar spectrum. Stars both on and off the main sequence are discussed in terms of distances, intrinsic properties, lifetimes and evolution. The Milky Way is compared to other galaxies in size, star population and structure, and the different galaxy shapes are pictured. Topics of most recent interest are covered by results of the lunar explorations, new concepts of Mars, and problems of space travel. Problems of modern astronomy include pulsars, neutron stars, and quasars.

Brandt, J. C.↗
NASA NTRS1982

Theoretical problems of spiral galaxies

Three theoretical problems concerning the large scale structure of disk galaxies in general, and the Milky Way System, in particular, were proposed to study. They are, namely, modes of spiral density waves, evolutionary change of the abundance distribution of the gas in the Milky Way System and the motions of the cloud medium behind the large scale galactic shock.

Yuan, C.↗
NASA NTRS1994

A comparison of dynamical and molecular gas masses in very luminous infrared galaxies

Observations of the 2.3 micron bands of CO have been used to measure the central stellar velocity dispersions in NGC 1614 and IC 694. K-band images were used to constrain models of the stellar mass distribution. With these data and a spectrum of Arp 220 from the literature, we have determined the total mass within the central regions of all three galaxies. The central molecular gas masses inferred from (12)CO J = 1-0 fluxes are larger than the total masses determined from stellar kinematics. Subtraction of the likely stellar mass from the total mass yields upper limits for the H2 mass that are 4-10 times less than the previously reported masses. This result supports other arguments that the I(sub CO)/M(sub H2) ratio is not the same in ultraluminous galaxies as it is in Milky Way giant molecular clouds.

Shier, L. M.↗
NASA NTRS2000

Tape Measure to the Stars

Calculating distances is one of the thorniest issues of astronomy. But now there are two new, promising methods that may serve as useful yardsticks. The Chandra X-ray Observatory has demonstrated a way to measure distances within the Milky Way and perhaps to nearby galaxies by measuring the delays of X-ray photons as they scatter off intervening matter. The late Compton Gamma-Ray Observatory, through its exhaustive archive of 2,700 gamma-ray bursts, has revealed patterns in these flashes of light that correspond to cosmological distances.

Wanjek, Christopher↗
NASA NTRS2003

First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Emission

The WMAP mission has mapped the full sky to determine the geometry, content, and evolution of the universe. Full sky maps are made in five microwave frequency bands to separate the temperature anisotropy of the cosmic microwave background (CMB) from foreground emission, including diffuse Galactic emission and Galactic and extragalactic point sources. We define masks that excise regions of high foreground emission, so CMB analyses can became out with minimal foreground contamination. We also present maps and spectra of the individual emission components, leading to an improved understanding of Galactic astrophysical processes. The effectiveness of template fits to remove foreground emission from the WMAP data is also examined. These efforts result in a CMB map with minimal contamination and a demonstration that the WMAP CMB power spectrum is insensitive to residual foreground emission. We use a Maximum Entropy Method to construct a model of the Galactic emission components. The observed total Galactic emission matches the model to less than 1% and the individual model components are accurate to a few percent. We find that the Milky Way resembles other normal spiral galaxies between 408 MHz and 23 GHz, with a synchrotron spectral index that is flattest (beta(sub s) approx. -2.5) near star-forming regions, especially in the plane, and steepest (beta(sub s) approx. -3) in the halo. This is consistent with a picture of relativistic cosmic ray electron generation in star-forming regions and diffusion and convection within the plane. The significant synchrotron index steepening out of the plane suggests a diffusion process in which the halo electrons are trapped in the Galactic potential long enough to suffer synchrotron and inverse Compton energy losses and hence a spectral steepening. The synchrotron index is steeper in the WMAP bands than in lower frequency radio surveys, with a spectral break near 20 GHz to beta(sub s) less than -3. The modeled thermal dust spectral index is also steep in the WMAP bands, with beta(sub d) approx. = 2.2. Our model is driven to these conclusions by the low level of total foreground contamination at approx. 60 GHz. Microwave and Ha measurements of the ionized gas agree well with one another at about the expected levels. Spinning dust emission is limited to less than 5% of the Ka-band foreground emission. A catalog of 208 point sources is presented. The reliability of the catalog is 98%, i.e., we expect five of the 208 sources to be statistically spurious. The mean spectral index of the point sources is alpha approx. 0(beta approx. -2). Derived source counts suggest a contribution to the anisotropy power from unresolved sources of (15.0 +/- 1.4) x 10(exp -3)micro sq K sr at Q-band and negligible levels at V-band and W-band. The Sunyaev-Zeldovich effect is shown to be a negligible "contamination" to the maps.

Bennett, C. L.↗
NASA NTRS2005

The locations of cosmic explosions

When massive stars exhaust their fuel they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. Recently, it has become apparent that stellar collapse can power the even more brilliant relativistic explosions known as long-duration gamma-ray bursts. In some cases, a gamma-ray burst and a supernova have been observed from the same event. One would thus expect that gamma-ray bursts and supernovae should be found in similar environments. Here we show that this expectation is wrong. Using Hubble Space Telescope imaging of the host galaxies of long-duration gamma-ray bursts and core-collapse supernovae, we demonstrate that while the distribution of the supernovae in their hosts traces the blue light of young stars, the gamma-ray bursts are much more concentrated on the very brightest regions of their hosts. Furthermore, the host galaxies of the gamma-ray bursts are significantly fainter and more irregular than the hosts of the supernovae. Together these results suggest that long-duration gamma-ray bursts are associated with the very most massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long-duration gamma-ray bursts are relatively rare in galaxies such as our own Milky Way.

Fruchter, A. S.↗
NASA NTRS2007

Hubble 2006: Science Year in Review

The 10 science articles selected for this years annual science report exemplify the range of Hubble research from the Solar System, across our Milky Way, and on to distant galaxies. The objects of study include a new feature on Jupiter, binaries in the Kuiper Belt, Cepheid variable stars, the Orion Nebula, distant transiting planets, lensing galaxies, active galactic nuclei, red-and-dead galaxies, and galactic outflows and jets. Each narrative strives to construct the readers understanding of the topics and issues, and to place the latest research in historical, as well as scientific, context. These essays reveal trends in the practice of astronomy. More powerful computers are permitting astronomers to study ever larger data sets, enabling the discovery of subtle effects and rare objects. (Two investigations created mosaic images that are among the largest produced to date.) Multiwavelength data sets from ground-based telescopes, as well as other great observatories Spitzer and Chandraare increasingly important for holistic interpretations of Hubble results. This yearbook also presents profiles of 12 individuals who work with Hubble, or Hubble data, on a daily basis. They are representative of the many students, scientists, engineers, and other professions who are proudly associated with Hubble. Their stories collectively communicate the excitement and reward of careers related to space science and technology.

Hubble space telescope↗
DOE OSTI2026

The DECam MAGIC Survey $-$ Mapping the Ancient Galaxy in CaHK: Overview and Summary of Early Science

We present the DECam Mapping the Ancient Galaxy in CaHK (MAGIC) survey, a 54-night NOIRLab Survey Program to image $\gtrsim$5,000$\,$deg$^2$ of the southern hemisphere using a metallicity-sensitive narrow-band filter covering the Ca$\,$ii$\,$H&K lines centered at 3955$\,$A. This filter is installed on the Dark Energy Camera (DECam), mounted on the 4-m NSF Víctor M. Blanco Telescope. The survey reaches typical $10σ$ depths of $\text{mag}_{\text{CaHK}} \approx 22.5$, 3$-$4$\,$mag deeper than comparable surveys in the southern hemisphere. By combining photometry from this Ca$\,$ii$\,$H&K filter with existing DECam $g,r,i$ broadband photometry from the DECam Local Volume Exploration (DELVE) survey, MAGIC is deriving photometric metallicities for red giant branch stars down to the magnitude limit of usable proper motions from Gaia data release 3 (DR3). MAGIC has already imaged $\sim$3,000$\,$deg$^2$, supplemented by other affiliated observing programs that have used this filter to image star clusters, dwarf galaxies, and stellar streams. We overview MAGIC's survey strategy, describe data processing through the derivation of metallicities and photometric distances, and summarize early science results that have been published with this dataset. In addition, we present several new results, including the confirmation of a distant ($>5\,r_h$) member of the Reticulum II ultra-faint dwarf galaxy, on-sky density maps of low-metallicity stars into the distant Milky Way halo ($\sim150\,$kpc) recovering 13/14 ultra-faint dwarf galaxies in the current footprint, and a validation of our initial targeting of extremely metal-poor stars. Collectively, these results demonstrate that the MAGIC dataset enables cutting-edge studies of the faint, low-metallicity regime of the Milky Way and its substructures.

Chiti, A. [KIPAC, Menlo Park] (ORCID:0000000271556↗
NASA NTRS2007

The Beginning and End of the Universe

Cosmology is the scientific study of how the Universe began more than 13 billion years ago, how its properties have changed, and what its future might be. The balance of forces and energy cause the Universe to expand, first accelerating, then decelerating and then accelerating again. Within this overall structure, the interplay of atoms and light with the mysterious dark matter and dark energy causes stars and galaxies to form and evolve, leading to galaxies like our own home, the Milky Way. Observational cosmology uses telescopes on Earth and in space to reach back in time to find the faint remaining echoes of the Big Bang and to trace the formation and evolution of the galaxies and structures that fill the Universe. In this lecture, Dr. Gardner will give an overview of cosmology, outlining the 13-billion year history of the Universe, and highlighting the very rapid progress this field has made in the last decade. He will discuss the role that NASA space telescopes have played in this progress and will continue to play in the years to come. He will give a time-based history of the Universe, discussing the successive processes that formed matter, particles, atoms, stars and galaxies. In particular, he will focus on cosmological inflation, the rapid accelerated expansion that marks the beginning of the Universe, and dark energy, a tenuous substance that overcomes gravity and whose properties will determine its final fate.

Gardner, Jonathan P.↗
NASA NTRS2008

The Beginning and End of the Universe

Cosmology is the scientific study of how the Universe began more than 13 billion years ago, how its properties have changed, and what its future might be. The balance of forces and energy cause the Universe to expand, first accelerating, then decelerating and then accelerating again. Within this overall structure, the interplay of atoms and light with the mysterious dark matter and dark energy causes stars and galaxies to form and evolve, leading to galaxies like our own home, the Milky Way. Observational cosmology uses telescopes on Earth and in space to reach back in time to find the faint remaining echoes of the Big Bang and to trace the formation and evolution of the galaxies and structures that fill the Universe. In this lecture, Dr. Gradner will give an overview of cosmology, outlining the 13-billion year history of the Universe, and highlighting the very rapid progress this field has made i the last decade. He will discuss the role that NASA space telescopes have played in this progress and wil continue to play in the years to come. He will give a time-based history of the Universe, discussing the successive processes that formed matter, particles, atoms, stars and galaxies. In particular, he will focus on cosmological inflation, the rapid accelerated expansion that marks the beginning of the Universe, and dark energy, a tenuous substance that overcomes gravity and whose properties will determine its final fate.

Gardner, Jonathan↗
NASA NTRS2003

Post-AGB Stars in Nearby Galaxies as Calibrators for HST

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program under Grant NAG 5-6821. The Principal Investigator is Howard E. Bond (Space Telescope Science Institute). STScI Postdoctoral Associates Laura K. Fullton (1998), David Alves (1998-2001), and Michael Siegel (2001) were partially supported by this grant. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic- giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The argument is that, in old populations, the stars that are evolving through the PAGB region of the HR diagram arise from only a single main-sequence turnoff mass. In addition, theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, PAGB stars of these spectral types are very easily identified. because of their large Balmer jumps, which are due to their very low surface gravities. Our approach is first to identify PAGB stars in Milky Way globular clusters and in other Local Group galaxies, which are at known distances, and thus to measure accurate absolute magnitudes for the PAGB stars. With this Milky Way and Local Group luminosity calibration, we will then be in a position to find PAGB stars in more distant galaxies from the ground, and ultimately from the Hubble Space Telescope. and thus derive distances. These PAGB stars are, as noted above, the visually brightest members of Population II, and hence will allow distance measurements to galaxies that do not contain Cepheids, such as elliptical galaxies, as well as distances to spirals using PAGB stars in their halos. Moreover, the method is entirely independent of Cepheids. and thus provides a direct test of the Cepheid distance scale. The program will also provide information on the evolutionary lifetimes of PAGB stars.

Bond, Howard E.↗
DOE OSTI2024

Asymmetric drift in MaNGA: mass and radially dependent stratification rates in galaxy discs

ABSTRACT We measure the age–velocity relationship from the lag between ionized gas and stellar tangential speeds in ∼500 nearby disc galaxies from MaNGA in Sloan Digital Sky Survey IV (SDSS-IV). Selected galaxies are kinematically axisymmetric. Velocity lags are asymmetric drift, seen in the Milky Way’s (MW) solar neighbourhood and other Local Group galaxies; their amplitude correlates with stellar population age. The trend is qualitatively consistent in rate ($\dot{\sigma }$) with a simple power-law model where σ ∝ tb that explains the dynamical phase-space stratification in the solar neighbourhood. The model is generalized based on disc dynamical times to other radii and other galaxies. We find in-plane radial stratification parameters σ0,r (dispersion of the youngest populations) in the range of 10–40 km s−1 and 0.2 < br < 0.5 for MaNGA galaxies. Overall, brincreases with galaxy mass, decreases with radius for galaxies above 10.4 dex (M⊙) in stellar mass, but is ∼constant with radius at lower mass. The measurement scatter indicates the stratification model is too simple to capture the complexity seen in the data, unsurprising given the many possible astrophysical processes that may lead to stellar population dynamical stratification. None the less, the data show dynamical stratification is broadly present in the galaxy population, with systematic trends in mass and density. The amplitude of the asymmetric drift signal is larger for the MaNGA sample than the MW, and better represented in the mean by what is observed in the discs of M31 and M33. Either typical discs have higher surface-density or, more likely, are dynamically hotter (hence thicker) than the MW.

Bershady, Matthew A. (ORCID:0000000231314374)↗