165 research outputs found
Optical spectroscopy of two overlapping, flux-density-limited samples of radio sources in the North Ecliptic Cap, selected at 38 MHz and 151 MHz
We present the results of optical spectroscopy of two flux-density-limited
samples of radio sources selected at frequencies of 38 and 151 MHz in the same
region around the North Ecliptic Cap, the 8C-NEC and 7C-III samples
respectively. Both samples are selected at flux density levels ~20 times
fainter than samples based on the 3C catalogue. They are amongst the first
low-frequency selected samples with no spectral or angular size selection for
which almost complete redshift information has been obtained and they will
therefore provide a valuable resource for understanding the cosmic evolution of
radio sources and their hosts and environments. The 151-MHz 7C-III sample is
selected to have S_151 >=0.5 Jy and is the more spectroscopically complete; out
of 54 radio sources fairly reliable redshifts have been obtained for 44
objects. The 8C sample has a flux limit of S_38 >=1.3 Jy and contains 58
sources of which 46 have fairly reliable redshifts. We discuss possible biases
in the observed redshift distribution, and some interesting individual objects.
Using the 8C-NEC and 7C-III samples in conjunction, we form the first sample
selected on low-frequency flux in the rest-frame of the source, rather than the
usual selection on flux density in the observed frame. This allows us to remove
the bias associated with an increasing rest-frame selection frequency with
redshift. We investigate the difference this selection makes to correlations of
radio source properties with redshift and luminosity. We show in particular
that flux-density-based selection leads to an overestimate of the steepness of
the correlation of radio source size with redshift. (abridged)Comment: 22 pages, 10 figures, accepted by MNRA
A Serendipitous Search for High-Redshift Lyman alpha Emission: Two Primeval Galaxy Candidates at z~3
In the course of our ongoing search for serendipitous high-redshift Lyman
alpha (LyA) Emissionin deep archival Keck spectra, we discovered two very high
equivalent width (W_{obs} ~ 450A, 2-sigma) LyA emission line candidates at z ~3
in a moderate dispersion (R~1200) spectrogram. Both lines have low velocity
dispersions (sigma_v ~ 60 km/s) and deconvolved radii r ~ 1 kpc (h = 0.5). We
argue that the lines are LyA, and are powered by stellar ionization. The
surface density of robust, high equivalent width LyA candidates is estimated to
be ~3 \pm 2 per arcmin^2 per unit redshift at z ~ 3, consistent with the
estimate of Cowie etal (1998). The LyA emission line source characteristics are
consistent with the galaxies undergoing their first burst of star formation,
ie, with being primeval. Source sizes and velocity dispersions are comparable
to the theoretical primeval galaxy model of Lin and Murray (1992) based on the
inside-out, self-similar collapse of an isothermal sphere. In this model, star
formation among field galaxies is a protracted process. Galaxies are thought to
be able to display high equivalent widths for only the first few x 10 Myr. This
time is short in relation to the difference in look back times between z=3 and
z=4, and implies that a substantial fraction of strong line-emitting galaxies
at z=3 were formed at redshifts z < 4. We discuss the significance of
high-equivalent width LyA-emitting galaxies in terms of the emerging picture of
the environment, and the specific characteristics of primeval galaxy formation
at high redshift.Comment: 17 pages, 3 figures, one table. To appear in the Astrophysical
Journa
One-Line Redshifts and Searches for High-Redshift Lyman-Alpha Emission
We report the serendipitous discovery of two objects close in projection with
fairly strong emission lines at long wavelength (~9190 A). One (A) seems not to
be hosted by any galaxy brighter than V(555)=27.5, or I(814)=26.7 (Vega-based
3-sigma limits in 1.0 arcsec diameter apertures), while the other line is
associated with a faint (I(814)~24.4) red galaxy (B) offset by 2.7 arcsec and 7
A spectrally. Both lines are broad (FWHM 700 km/s), extended spatially, and
have high equivalent widths (W(A,obs)>1225 A, 95% confidence limit;
W(B,obs)~150 A). No secondary spectral features are detected for galaxy A. Blue
continuum and the marginal detection of a second weak line in the spectrum of
galaxy B is consistent with [OII] (the strong line) and MgII (the weak line) at
z=1.466. By association, galaxy A is likely at z=1.464, implying a rest-frame
equivalent width of the [OII] emission line in excess of 600 A and a projected
separation of 30 kpc for the galaxy pair. Conventional wisdom states that
isolated emission lines with rest-frame equivalent widths larger than ~200 A
are almost exclusively Lyman-alpha. This moderate-redshift discovery therefore
compromises recent claims of high-redshift Lyman-alpha emitters for which other
criteria (i.e., line profile, associated continuum decrements) are not
reported. We discuss observational tests to distinguish Lyman-alpha emitters at
high redshift from foreground systems.Comment: 16 pages, 3 figures; to appear in The Astrophysical Journal (July 1,
2000
A z=5.34 Galaxy Pair in the Hubble Deep Field
We present spectrograms of the faint V-drop (V(606) = 28.1, I(814) = 25.6)
galaxy pair HDF3-951.1 and HDF3-951.2 obtained at the Keck II Telescope.
Fernandez-Soto, Lanzetta, & Yahil (1998) derive a photometric redshift of z(ph)
= 5.28 (+0.34,-0.41; 2 sigma) for these galaxies; our integrated spectrograms
show a large and abrupt discontinuity near 7710 (+- 5) Angstroms. This break is
almost certainly due to the Lyman alpha forest as its amplitude (1 - fnu(short)
/ fnu(long) > 0.87; 95% confidence limit) exceeds any discontinuities observed
in stellar or galaxian rest-frame optical spectra. The resulting
absorption-break redshift is z=5.34 (+- 0.01). Optical/near-IR photometry from
the HDF yields an exceptionally red (V(606)-I(814)) color, consistent with this
large break. A more accurate measure of the continuum depression blueward of
Lyman alpha utilizing the imaging photometry yields D(A) = 0.88.
The system as a whole is slightly brighter than L*(1500) relative to the z~3
Lyman break population and the total star formation rate inferred from the UV
continuum is ~22 h(50)^-2 M(sun) yr^-1 (q(0) = 0.5) assuming the absence of
dust extinction. The two individual galaxies are quite small (size scales < 1
h(50)^-1 kpc). Thus these galaxies superficially resemble the Pascarelle etal
(1996) ``building blocks''; if they comprise a gravitationally bound system,
the pair will likely merge in a time scale ~100 Myr.Comment: 18 pages, 4 figures; accepted to A
Design of a vehicle based system to prevent ozone loss
Reduced quantities of ozone in the atmosphere allow greater levels of ultraviolet light (UV) radiation to reach the earth's surface. This is known to cause skin cancer and mutations. Chlorine liberated from Chlorofluorocarbons (CFC's) and natural sources initiate the destruction of stratospheric ozone through a free radical chain reaction. The project goals are to understand the processes which contribute to stratospheric ozone loss, examine ways to prevent ozone loss, and design a vehicle-based system to carry out the prevention scheme. The 1992/1993 design objectives were to accomplish the first two goals and define the requirements for an implementation vehicle to be designed in detail starting next year. Many different ozone intervention schemes have been proposed though few have been researched and none have been tested. A scheme proposed by R.J. Cicerone, Scott Elliot and R.P.Turco late in 1991 was selected because of its research support and economic feasibility. This scheme uses hydrocarbon injected into the Antarctic ozone hole to form stable compounds with free chlorine, thus reducing ozone depletion. Because most polar ozone depletion takes place during a 3-4 week period each year, the hydrocarbon must be injected during this time window. A study of the hydrocarbon injection requirements determined that 100 aircraft traveling Mach 2.4 at a maximum altitude of 66,000 ft. would provide the most economic approach to preventing ozone loss. Each aircraft would require an 8,000 nm. range and be able to carry 35,000 lbs. of propane. The propane would be stored in a three-tank high pressure system. Missions would be based from airport regions located in South America and Australia. To best provide the requirements of mission analysis, an aircraft with L/D(sub cruise) = 10.5, SFC = 0.65 (the faculty advisor suggested that this number is too low) and a 250,000 lb TOGW was selected as a baseline. Modularity and multi-role functionality were selected to be key design features. Modularity provides ease of turnaround for the down-time critical mission. Multi-role functionality allows the aircraft to be used beyond its design mission, perhaps as an High Speed Civil Transport (HSCT) or for high altitude research
A Lyman-alpha-only AGN from the Sloan Digital Sky Survey
The Sloan Digital Sky Survey has discovered a z=2.4917 radio-loud active
galactic nucleus (AGN) with a luminous, variable, low-polarization UV
continuum, H I two-photon emission, and a moderately broad Lyman-alpha line
(FWHM = 1430 km/s) but without obvious metal-line emission. SDSS
J113658.36+024220.1 does have associated metal-line absorption in three
distinct, narrow systems spanning a velocity range of 2710 km/s. Despite
certain spectral similarities, SDSS J1136+0242 is not a Lyman-break galaxy.
Instead, the Ly-alpha and two-photon emission can be attributed to an extended,
low-metallicity narrow-line region. The unpolarized continuum argues that we
see SDSS J1136+0242 very close to the axis of any ionization cone present. We
can conceive of two plausible explanations for why we see a strong UV continuum
but no broad-line emission in this `face-on radio galaxy' model for SDSS
J1136+0242: the continuum could be relativistically beamed synchrotron emission
which swamps the broad-line emission; or, more likely, SDSS J1136+0242 could be
similar to PG 1407+265, a quasar in which for some unknown reason the
high-ionization emission lines are very broad, very weak, and highly
blueshifted.Comment: AJ, in press, 10 pages emulateapj forma
HPV infection and immunochemical detection of cell-cycle markers in verrucous carcinoma of the penis
Penile verrucous carcinoma is a rare disease and little is known of its aetiology or pathogenesis. In this study we examined cell-cycle proteins expression and correlation with human papillomavirus infection in a series of 15 pure penile verrucous carcinomas from a single centre. Of 148 penile tumours, 15 (10%) were diagnosed as pure verrucous carcinomas. The expression of the cell-cycle-associated proteins p53, p21, RB, p16INK4A and Ki67 were examined by immunohistochemistry. Human papillomavirus infection was determined by polymerase chain reaction to identify a wide range of virus types. The expression of p16INK4A and Ki67 was significantly lower in verrucous carcinoma than in usual type squamous cell carcinoma, whereas the expression of p53, p21 and RB was not significantly different. p53 showed basal expression in contrast to usual type squamous cell carcinoma. Human papillomavirus infection was present in only 3 out of 13 verrucous carcinomas. Unique low-risk, high-risk and mixed viral infections were observed in each of the three cases. In conclusion, lower levels of p16INK4A and Ki67 expressions differentiate penile verrucous carcinoma from usual type squamous cell carcinoma. The low Ki67 index reflects the slow-growing nature of verrucous tumours. The low level of p16INK4A expression and human papillomavirus detection suggests that penile verrucous carcinoma pathogenesis is unrelated to human papillomavirus infection and the oncogenes and tumour suppressor genes classically altered by virus infection.Peer reviewedFinal Accepted Versio
JADES: Using NIRCam Photometry to Investigate the Dependence of Stellar Mass Inferences on the IMF in the Early Universe
The detection of numerous and relatively bright galaxies at redshifts z > 9
has prompted new investigations into the star-forming properties of
high-redshift galaxies. Using local forms of the initial mass function (IMF) to
estimate stellar masses of these galaxies from their light output leads to
galaxy masses that are at the limit allowed for the state of the LambdaCDM
Universe at their redshift. We explore how varying the IMF assumed in studies
of galaxies in the early universe changes the inferred values for the stellar
masses of these galaxies. We infer galaxy properties with the SED fitting code
Prospector using varying IMF parameterizations for a sample of 102 galaxies
from the JWST Advanced Deep Extragalactic Survey (JADES) spectroscopically
confirmed to be at z > 6.7, with additional photometry from the JWST
Extragalactic Medium Band Survey (JEMS) for twenty-one galaxies. We demonstrate
that models with stellar masses reduced by a factor of three or more do not
affect the modeled spectral energy distribution (SED).Comment: The Significance statement is required for PNAS submissio
The JWST Extragalactic Mock Catalog: Modeling Galaxy Populations from the UV through the Near-IR over 13 Billion Years of Cosmic History
We present an original phenomenological model to describe the evolution of galaxy number counts, morphologies, and spectral energy distributions across a wide range of redshifts (0.26]. Our model follows observed mass and luminosity functions of both star-forming and quiescent galaxies, and reproduces the redshift evolution of colors, sizes, star-formation and chemical properties of the observed galaxy population. Unlike other existing approaches, our model includes a self-consistent treatment of stellar and photoionized gas emission and dust attenuation based on the BEAGLE tool. The mock galaxy catalogs generated with our new model can be used to simulate and optimize extragalactic surveys with future facilities such as the James Webb Space Telescope (JWST), and to enable critical assessments of analysis procedures, interpretation tools, and measurement systematics for both photometric and spectroscopic data. As a first application of this work, we make predictions for the upcoming JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations teams. We show that JADES will detect, with NIRCam imaging, thousands of galaxies at z>6, and tens at z>10 at m_AB8, and resolve the current debate about the rate of evolution of galaxies at z>8. Ready to use mock catalogs and software to generate new realizations are publicly available as the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) package.ECL, JC and SCh acknowledge support from the European Research Council (ERC) via an Advanced Grant under grant agreement no. 321323- NEOGAL. CCW acknowledges support from the National Science Foundation Astronomy and Astrophysics Fellowship grant AST-1701546. SCh acknowledges financial support from the Science and Technology Facilities Council (STFC). All members of NIRCam (CCW, KNH, BER, RE, DPS, CNAW, SAl, SB, SCr, EE, DJE, MR) acknowledge funding from JWST/NIRCam contract to the University of Arizona, NAS5-02015. BER acknowledges partial support through NASA contract NNG16PJ25C, grants 17-ATP17- 0034 and HST-GO-14747. SAr is funded by MINECO under grant ESP2015-68964-P. RM and RA acknowledge ERC Advanced Grant 695671 "QUENCH” and support by the Science and Technology Facilities Council (STFC). RS acknowledges a NWO Rubicon grant, project number 680-50- 1518. This work is based on observations taken by the CANDELS Multi-cycle Treasury Program with the NASA/ESA HST
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