448 research outputs found
The Challenge to Large Optical Telescopes from X-ray Astronomy
In the ROSAT era of the mid-1990's, the problems facing deep X-ray surveys
could be largely solved with 10 m class telescopes. In the first decade of this
new millennium, with X-ray telescopes such as the Chandra X-ray Observatory and
XMM-Newton in operation, deep X-ray surveys are challenging 10 m telescopes.
For example, in the Chandra Deep Field surveys, approximately 30% of the X-ray
sources have optical counterparts fainter than R=25 (I=24).
This paper reviews current progress with 6-10 m class telescopes in following
up sources discovered in deep X-ray surveys, including results from several
X-ray surveys which have depended on telescopes such as Keck, VLT and HET.
Topics include the prospects for detecting extreme redshift (z>6) quasars and
the first detections of normal and starburst galaxies at cosmologically
interesting distances in the X-ray band.
X-ray astronomy can significantly bolster the science case for the next
generation of large aperture (30-100 m) ground-based telescopes and has already
provided targets for these large telescopes through the Chandra and XMM-Newton
surveys. The next generation of X-ray telescopes will continue to challenge
large optical telescopes; this review concludes with a discussion of prospects
from new X-ray missions coming into operation on a 5-30 year timescale.Comment: 15 pages, 6 figures, Invited review for SPIE conference "Science with
6-10 m Class Telescopes
X-Ray Binary Populations in a Cosmological Context, Including NuSTAR Predictions
The new ultradeep 4 Ms Chandra Deep Field South has afforded the deepest view ever of X-ray binary populations. We report on the latest results on both LMXB and HMXB evolution out to redshifts of approximately four, including comparison with the latest theoretical models, using this deepest-ever view of the X-ray universe with Chandra. The upcoming NuSTAR mission will open up X-ray binary populations in the hard X-ray band, similar to the pioneering work of Fabbiano et al. in the Einstein era. We report on plans to study both Local Group and starburst galaxies as well as the implications those observations may have for X-ray binary populations in galaxies contributing to the Cosmic X-ray Background
Studying Dark Energy, Black Holes and Cosmic Feedback at X-ray Wavelengths: NASA's Constellation-X Mission
Among the most important topics in modern astrophysics are the nature of the dark energy equation of state, the formation and evolution of supermassive black holes in concert with galaxy bulges, and the self-regulating symmetry imposed by both stellar and AGN feedback. All of these topics are readily addressed with observations at X-ray wavelengths. For instance, theoretical models predict that the majority (98%) of the energy and metal content in starburst superwinds exists in the hot million-degree gas. The Constellation-X observatory is being developed to perform spatially resolved high-resolution X-ray spectroscopy so that we may directly measure the absolute element abundances and velocities of this hot gas. This talk focuses on the driving science behind this mission, which is one of two flagship missions in NASA's Beyond Einstein program. A general overview of the observatory's capabilities and basic technology will also be given
Sites of Agency, Sites of Growth: Elements of Success for Formerly Incarcerated Adult Graduates of an Alternative High School
Students who leave high school before graduating run a high risk of becoming incarcerated, and adults with a record of incarceration and no high school diploma have difficulty maintaining legal employment and therefore remaining out of prison. For adults who lack high school diplomas, few options exist to earn that credential. Though standardized testing is still a point of controversy in education policy for juveniles, the GED exam is the assumed standard for adults in the United States to earn their high school credentials, and few alternatives exist for those who are ill-equipped to pass a demanding standardized test. This qualitative case study of two graduates of an alternative, non-test-based high school for formerly incarcerated adults in Chicago explores how the post-incarceration experiences and geographical locations of those graduates impact their lifestyle choices. The two research subjects interviewed are both formerly incarcerated adults who have beaten the odds of recidivism by remaining out of prison for more than three years and securing stable employment. Research was conducted via semistructured one-on-one interviews with the subjects over a period of 20 months. The study explores the effect of Bronfenbrenner’s ecological systems theory on low-income urban youth of color and the adults they eventually became. The study found that, while these students were negatively impacted by nested systems during their childhoods, some of the effect of these systems – poor schooling systems, lack of parental support and over-zealous policing – were ameliorated by an appropriate, supportive parole placement that emphasized education for the sake of personal transformation
Deep GALEX Observations of the Coma Cluster: Source Catalog and Galaxy Counts
We present a source catalog from deep 26 ks GALEX observations of the Coma
cluster in the far-UV (FUV; 1530 A) and near-UV (NUV; 2310 A) wavebands. The
observed field is centered 0.9 deg (1.6 Mpc) south-west of the Coma core, and
has full optical photometric coverage with SDSS. The catalog consists of 9700
galaxies with GALEX and SDSS photometry, including 242
spectroscopically-confirmed Coma member galaxies that range from giant spirals
and elliptical galaxies to dwarf irregular and early-type galaxies. The full
multi-wavelength catalog (cluster plus background galaxies) is ~80% complete to
NUV=23 and FUV=23.5, and has a limiting depth at NUV=24.5 and FUV=25.0 which
corresponds to a star formation rate of ~0.001 Msun/yr at the distance of Coma.
Our deep GALEX observations required a two-fold approach to generating a source
catalog: we used a Bayesian deblending algorithm to measure faint and compact
sources (using SDSS coordinates as a position prior), and relied on the GALEX
pipeline catalog for bright/extended objects. We performed simulations to
assess the influence that systematic effects (e.g. object blends, source
confusion, Eddington Bias) have on source detection and photometry when using
both methods. The Bayesian deblending method roughly doubles the number of
source detections and provides reliable photometry to a few magnitudes deeper
than the GALEX pipeline catalog. This method is also free from source confusion
over the UV magnitude range studied here; conversely, we estimate that the
GALEX pipeline catalogs are confusion limited at magnitudes fainter than NUV~23
and FUV~24. We have measured the total UV galaxy counts using our catalog and
report a ~50% excess of counts across FUV=22-23.5 and NUV=21.5-23 relative to
previous GALEX measurements, which is not attributed to cluster member
galaxies. Our galaxy counts are a better match to deeper UV counts measured
with HST.Comment: 27 pages, 13 figures, 4 tables, accepted for publication in ApJ
The Relationship of Hard X-ray and Optical Line Emission in Low Redshift Active Galactic Nuclei
In this paper we assess the relationship of the population of Active Galactic
Nuclei (AGN) selected by hard X-rays to the traditional population of AGN with
strong optical emission lines. First, we study the emission-line properties of
a new hard X-ray selected sample of 47 local AGN (classified optically as both
Type 1 and Type 2 AGN). We find that the hard X- ray (3-20 keV) and
[OIII]5007 optical emission-line luminosities are well-correlated over
a range of about four orders-of-magnitude in luminosity (mean luminosity ratio
2.15 dex with a standard deviation of = 0.51 dex). Second, we study
the hard X-ray properties of a sample of 55 local AGN selected from the
literature on the basis of the flux in the [OIII] line. The correlation between
the hard X-ray (2-10 keV) and [OIII] luminosity for the Type 1 AGN is
consistent with what is seen in the hard X-ray selected sample. However, the
Type 2 AGN have a much larger range in the luminosity ratio, and many are very
weak in hard X-rays (as expected for heavily absorbed AGN). We then compare the
hard X-ray (3-20 keV) and [OIII] luminosity functions of AGN in the local
universe. These have similar faint-end slopes with a luminosity ratio of 1.60
dex (0.55 dex smaller than the mean value for individual hard X-ray selected
AGN). We conclude that at low redshift, selection by narrow optical emission-
lines will recover most AGN selected by hard X-rays (with the exception of BL
Lac objects). However, selection by hard X-rays misses a significant fraction
of the local AGN population with strong emission lines
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