536 research outputs found
Nuclear activity and the environments of nearby radio galaxies
Much of our present understanding of galaxy evolution over a large redshift range is based on the study of samples selected on the basis of non-thermal radio emission. It is therefore necessary to understand the relationship between radio source activity and the host galaxy. Recent observations suggest that there is a connection between radio galaxy (RG) activity and radio galaxy evolution. For example, high-redshift RGs (z approx. greater than 0.7) show evidence for significant populations of young stars, and have optical continuum morphologies nearly always aligned with the radio axis (McCarthy et al. 1987; Chambers et al. 1987). This phenomenon is generally attributed to radio jet induced star formation (DeYoung 1989), but the lack of high S/N spectra of the galaxy continua, and recent detections of polarized light in a few objects make it hard to rule out other processes such as scattering or synchrotron radiation. A detailed study of the continuum light in the distant RGs is difficult as they are optically very faint. However, nearby RGs (z approx. less than 0.1) have bluer B-V colors than radio-quiet ellipticals, presumably due to the presence of young stellar populations (Smith and Heckman 1989) and several have extended UV continuum emitting regions along their radio axes (van Bruegel et al. 1985a, b, di Serego Alighieri et al. 1989), reminiscent of the alignment effect seen in the high redshift RGs. We have almost completed a continuum imaging survey of nearby (and therefore optically brighter), powerful RGs to study any possible relationships between the optical continuum light and radio source activity. In particular we are interested in (1) whether these lower redshift RGs shown any evidence of the alignment effect (in their rest-frame UV light) that is seen in the distant RGs, and (2) the effects that the radio source has on the environment of the host galaxy
Keck Observations of the Most Distant Galaxy: 8C1435+63 at z=4.25
We report on Keck observations and confirm the redshift of the most distant
galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly line,
a Ly forest continuum break and a continuum break at
\AA. The Ly emission is spatially extended and
roughly aligned with the radio source. The galaxy shows a double structure in
the -band (1500\AA) which is aligned with the radio
axis; the two -band components spatially coincide with the nuclear and
southern radio components. Some fraction of the band emission could be due
to a nonthermal process such as inverse compton scattering. In the -band
(4200\AA), which may be dominated by starlight, the
galaxy has a very low surface brightness, diffuse morphology. The
morphology shows little relationship to the radio source structure, although
the major axis of the emission is elongated roughly in the direction of the
radio source axis. The galaxian continuum is very red () and if the
continuum is due to starlight, implies a formation redshift of . We
speculate that this galaxy may be the progenitor of a present day cD galaxy.Comment: 4 pages + 4 figures; uuencoded tar compressed PostScript files;
figures and tables included. To appear in 1 Jan 1995 issue of The
Astrophysical Journal, Letters. Please direct requests/questions/comments to
[email protected]
On the Automated and Objective Detection of Emission Lines in Faint-Object Spectroscopy
Modern spectroscopic surveys produce large spectroscopic databases, generally
with sizes well beyond the scope of manual investigation. The need arises,
therefore, for an automated line detection method with objective indicators for
detection significance. In this paper, we present an automated and objective
method for emission line detection in spectroscopic surveys and apply this
technique to 1574 spectra, obtained with the Hectospec spectrograph on the MMT
Observatory (MMTO), to detect Lyman alpha emitters near z ~ 2.7. The basic idea
is to generate on-source (signal plus noise) and off-source (noise only) mock
observations using Monte Carlo simulations, and calculate completeness and
reliability values, (C, R), for each simulated signal. By comparing the
detections from real data with the Monte Carlo results, we assign the
completeness and reliability values to each real detection. From 1574 spectra,
we obtain 881 raw detections and, by removing low reliability detections, we
finalize 649 detections from an automated pipeline. Most of high completeness
and reliability detections, (C, R) ~ (1.0, 1.0), are robust detections when
visually inspected; the low C and R detections are also marginal on visual
inspection. This method at detecting faint sources is dependent on the accuracy
of the sky subtraction.Comment: 19 pages, 16 figures, submitted to MNRA
Radio loud far-infrared galaxies
The first results are presented of a multiwavelength study of Infrared Astronomy Satellite (IRAS) galaxies with excess radio emission. The sample was selected by cross correlating the IRAS Faint Source Survey, and the Point Source Catalogue with the Texas radio survey. Recent optical (imaging and spectroscopic) and radio (VLA) observations are discussed. These observations will be used to investigate possible connections between radio galaxy activity, star formation and galaxy interactions
Overview of the DESI Legacy Imaging Surveys
The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing–Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg^2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorersatellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project
Spatially Resolved Gas Kinematics within a Ly Nebula: Evidence for Large-scale Rotation
We use spatially extended measurements of Ly as well as less
optically thick emission lines from an 80 kpc Ly nebula at
to assess the role of resonant scattering and to disentangle
kinematic signatures from Ly radiative transfer effects. We find that
the Ly, CIV, HeII, and CIII] emission lines all tell a similar story in
this system, and that the kinematics are broadly consistent with large-scale
rotation. First, the observed surface brightness profiles are similar in extent
in all four lines, strongly favoring a picture in which the Ly photons
are produced in situ instead of being resonantly scattered from a central
source. Second, we see low kinematic offsets between Ly and the less
optically thick HeII line (100-200 km s), providing further
support for the argument that the Ly and other emission lines are all
being produced within the spatially extended gas. Finally, the full velocity
field of the system shows coherent velocity shear in all emission lines:
500 km s over the central 50 kpc of the nebula. The
kinematic profiles are broadly consistent with large-scale rotation in a gas
disk that is at least partially stable against collapse. These observations
suggest that the Ly nebula represents accreting material that is
illuminated by an offset, hidden AGN or distributed star formation, and that is
undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of
M(<R=20 kpc) , this system may represent the
early formation of a large Milky Way mass galaxy or galaxy group.Comment: Accepted to ApJ; 25 pages in emulateapj format; 15 figures, 4 table
The Radio Galaxy 3C265 Contains a Hidden Quasar Nucleus
We report the discovery of broad MgII emission from the high redshift radio
galaxy 3C265 (z=0.81). We detect the broad line in the nuclear spectrum and in
the spatially extended galaxian component, both near the nucleus and in the
spectrum of an off-nuclear knot located 31 kpc south east of the nucleus of the
galaxy. These data provide strong support for the simplest form of the
unification hypothesis, that radio galaxies are quasars whose optical radiation
is directed in the plane of the sky rather than into our line of sight. These
data also strongly support the scattering model for the alignment of the UV
continuum emission with the radio axis. In 3C265, if the axis of the
anisotropically emitted UV continuum radiation is identified with the major
axis of the radio source, then the observed rest frame UV continuum emission
implies that the opening angle of the radiation cone is large (half angle
approximately 45 degrees). We also derive a mass estimate of 8x10^{10} Msun for
the central region of 3C265 from its rotation curve. The implied mass-to-light
ratio is low (M/L is roughly 2), and suggests that a significant fraction of
the rest frame UV continuum emission from this galaxy is dominated by
reprocessed radiation from the buried AGN. Finally, we detect the
CaII\lambda3933 K line in absorption in the integrated spectrum of 3C265. This
provides direct spectroscopic evidence for the existence of stars in a high
redshift radio galaxy.Comment: 26 pages (including figures) in gzip-ed uuencoded compressed
postscript format. Accepted for publication in ApJ, March 1, 1996 issu
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