46 research outputs found
Reimagining Near-Earth Space Policy in a Post-COVID World
Our planet and our species are at an existential crossroads. In the long term, climate change threatens to upend life as we know it, while the ongoing COVID-19 pandemic revealed that the world is unprepared and ill-equipped to handle acute shocks to its many systems. These shocks exacerbate the inequities and challenges already present prior to COVID in ways that are still evolving in unpredictable directions. As weary nations look toward a post-COVID world, we draw attention to both the injustice and many impacts of the quiet occupation of near-Earth space, which has rapidly escalated during this time of global crisis. The communities most impacted by climate change, the ongoing pandemic, and systemic racism are those whose voices are missing as stakeholders both on the ground and in space. We argue that significant domestic and international changes to the use of near-Earth space are urgently needed to preserve access to — and the future utility of — the valuable natural resources of space and our shared skies. After examining the failure of the U.S. and international space policy status quo to address these issues, we make specific recommendations in support of safer and more equitable uses of near-Earth space
Aggregate Effects of Proliferating Low-Earth-Orbit Objects and Implications for Astronomical Data Lost in the Noise
The rising population of artificial satellites and associated debris in low-altitude orbits is increasing the overall brightness of the night sky, threatening ground-based astronomy as well as a diversity of stakeholders and ecosystems reliant on dark skies. We present calculations of the potentially large rise in global sky brightness from space objects in low Earth orbit, including qualitative and quantitative assessments of how professional astronomy may be affected. Debris proliferation is of special concern: we calculate that all log-decades in debris size contribute approximately the same amount of night sky radiance, so debris-generating events are expected to lead to a rapid rise in night sky brightness along with serious collision risks for satellites from centimetre-sized objects. This increase in low-Earth-orbit traffic will lead to loss of astronomical data and diminish opportunities for ground-based discoveries as faint astrophysical signals become increasingly lost in the noise. Lastly, we discuss the broader consequences of brighter skies for a range of sky constituencies, equity/inclusion and accessibility for Earth- and space-based science, and cultural sky traditions. Space and dark skies represent an intangible heritage that deserves intentional preservation and safeguarding for future generations
Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
We present new constraints on the density profiles of dark matter (DM) halos
in seven nearby dwarf galaxies from measurements of their integrated stellar
light and gas kinematics. The gas kinematics of low mass galaxies frequently
suggest that they contain constant density DM cores, while N-body simulations
instead predict a cuspy profile. We present a data set of high resolution
integral field spectroscopy on seven galaxies and measure the stellar and gas
kinematics simultaneously. Using Jeans modeling on our full sample, we examine
whether gas kinematics in general produce shallower density profiles than are
derived from the stars. Although 2/7 galaxies show some localized differences
in their rotation curves between the two tracers, estimates of the central
logarithmic slope of the DM density profile, gamma, are generally robust. The
mean and standard deviation of the logarithmic slope for the population are
gamma=0.67+/-0.10 when measured in the stars and gamma=0.58+/-0.24 when
measured in the gas. We also find that the halos are not under concentrated at
the radii of half their maximum velocities. Finally, we search for correlations
of the DM density profile with stellar velocity anisotropy and other baryonic
properties. Two popular mechanisms to explain cored DM halos are an exotic DM
component or feedback models that strongly couple the energy of supernovae into
repeatedly driving out gas and dynamically heating the DM halos. We investigate
correlations that may eventually be used to test models. We do not find a
secondary parameter that strongly correlates with the central DM density slope,
but we do find some weak correlations. Determining the importance of these
correlations will require further model developments and larger observational
samples. (Abridged)Comment: 29 pages, 18 figures, 10 tables, accepted for publication in Ap
A Catalogue of Morphologically Classified Galaxies from the Sloan Digital Sky Survey: North Equatorial Region
We present a catalogue of morphologically classified bright galaxies in the
north equatorial stripe (230 deg) derived from the Third Data Release of
the Sloan Digital Sky Survey (SDSS). Morphological classification is performed
by visual inspection of images in the band. The catalogue contains 2253
galaxies complete to a magnitude limit of after Galactic extinction
correction, selected from 2658 objects that are judged as extended in the
photometric catalogue in the same magnitude limit. 1866 galaxies in our
catalogue have spectroscopic information. A brief statistical analysis is
presented for the frequency of morphological types and mean colours in the
catalogue. A visual inspection of the images reveals that the rate of
interacting galaxies in the local Universe is approximately 1.5% in the
sample. A verification is made for the photometric catalogue generated
by the SDSS, especially as to its bright end completeness.Comment: Accepted for publication in Astronomical Journal. Table 2 available
at http://www.icrr.u-tokyo.ac.jp/~fukugita/MCGpaper/table2.tx
Two Pseudobulges in the "Boxy Bulge" Galaxy NGC 5746
Galaxy formation and growth under the {\Lambda}CDM paradigm is expected to
proceed in a hierarchical, bottom-up fashion by which small galaxies grow into
large galaxies; this mechanism leaves behind large "classical bulges"
kinematically distinct from "pseudobulges" grown by internal, secular
processes. We use archival data (Spitzer 3.6 \mum wavelength, Hubble Space
Telescope H-band, Two Micron All Sky Survey Ks-band, and Sloan Digital Sky
Survey gri-band) to measure composite minor- and major-axis surface brightness
profiles of the almost-edgeon spiral galaxy NGC 5746. These light profiles span
a large range of radii and surface brightnesses to reveal an inner, high
surface brightness stellar component that is distinct from the well-known boxy
bulge. It is well fitted by S\'ersic functions with indices n = 0.99 \pm 0.08
and 1.17 \pm 0.24 along the minor and major axes, respectively. Since n < 2, we
conclude that this innermost component is a secularly-evolved pseudobulge that
is distinct from the boxy pseudobulge. This inner pseduobulge makes up 0.136
\pm 0.019 of the total light of the galaxy. It is therefore considerably less
luminous than the boxy structure, which is now understood to be a bar seen
nearly end-on. The infrared imagery shows further evidence for secular
evolution in the form of a bright inner ring of inner radius 9.1 kpc and width
1.6 kpc. NGC 5746 is therefore a giant, pure-disk SB(r)bc galaxy with no sign
of a merger-built bulge. We do not understand how such galaxies form in a
{\Lambda}CDM universe.Comment: 23 pages, 7 figures, 2 tables; accepted for publication in Ap
A Comparative Astrochemical Study Of The High-Mass Protostellar Objects NGC 7538 IRS 9 and IRS 1
We report the results of a spectroscopic study of the high-mass protostellar
object NGC 7538 IRS 9 and compare our observations to published data on the
nearby object NGC 7538 IRS 1. Both objects originated in the same molecular
cloud and appear to be at different points in their evolutionary histo- ries,
offering an unusual opportunity to study the temporal evolution of envelope
chemistry in objects sharing a presumably identical starting composition.
Observations were made with the Texas Echelon Cross Echelle Spectrograph
(TEXES), a sensitive, high spectral resolution (R = {\lambda}/{\Delta}{\lambda}
\simeq 100,000) mid-infrared grating spectrometer. Forty-six individual lines
in vibrational modes of the molecules C2H2, CH4, HCN, NH3 and CO were detected,
including two isotopologues (13CO, 12C18O) and one combination mode ({\nu}4 +
{\nu}5 C2H2). Fitting synthetic spectra to the data yielded the Doppler shift,
excitation temperature, Doppler b parameter, column density and covering factor
for each molecule observed; we also computed column density upper limits for
lines and species not detected, such as HNCO and OCS. We find differences among
spectra of the two objects likely attributable to their differing radiation and
thermal environments. Temperatures and column densities for the two objects are
generally consistent, while the larger line widths toward IRS 9 result in less
saturated lines than those toward IRS 1. Finally, we compute an upper limit on
the size of the continuum-emitting region (\sim2000 AU) and use this constraint
and our spectroscopy results to construct a schematic model of IRS 9.Comment: 23 pages, 15 figures, 6 tables; accepted for publication in Ap
SDSSJ103913.70+533029.7: A Super Star Cluster in the Outskirts of a Galaxy Merger
We describe the serendipitous discovery in the spectroscopic data of the
Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a
heliocentric radial velocity of +1012 km/s. Its proximity in position and
velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy.
At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star
cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and
photometric properties imply a mass of > 10^6 solar masses and an age close to
that of the tidal shells seen around NGC 3310, suggesting that it formed in the
event which formed the shells.Comment: Accepted by AJ: 4 figures (1 color
The Milky Way Tomography With SDSS. III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.NSF AST-615991, AST-0707901, AST-0551161, AST-02-38683, AST-06-07634, AST-0807444, PHY05-51164NASA NAG5-13057, NAG5-13147, NNXO-8AH83GPhysics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationMarie Curie Research Training Network ELSA (European Leadership in Space Astrometry) MRTN-CT-2006-033481Fermi Research Alliance, LLC, United States Department of Energy DE-AC02-07CH11359Alfred P. Sloan FoundationParticipating InstitutionsJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandMcDonald Observator