722 research outputs found
GENIE observations of small scale astrophysical processes in star forming regions and quasars
The VLTI/GENIE configuration will operate using at least 4 of the VLTI
telescopes (and possibly with one or more of the AT telescopes in the future if
adaptive optics become available on them). GENIE effectively can be thought of
as a 'smart' coronagraph, enabling high dynamic range imaging to be achieved at
moderate spatial resolution, with high rejection of the emission of a central
bright point source. However, but this bright source rejection may only provide
a rather moderate image quality (due to the few baselines and transfer function
on the sky). Operated in this way, only limited image reconstruction is
possible since classical radio and millimeter wavelength interferometry
techniques are not directly applicable to the outputs of optical
interferometers because the absolute phases are generally not measured.
However, measurements of visibility and closure phase could lead to situations
where image reconstruction becomes possible. This paper addresses the issue of
whether there are areas outside of the exoplanet search where it might be able
to make a useful impact on astronomy.Comment: Proceedings of the Genie-Darwin Workshop - Hunting for Planet
A multi-wavelength view of galaxy evolution with AKARI
AKARI's all-sky survey resolves the far-infrared emission in many thousands
of nearby galaxies, providing essential local benchmarks against which the
evolution of high-redshift populations can be measured. This review presents
some recent results in the resolved galaxy populations, covering some
well-known nearby targets, as well as samples from major legacy surveys such as
the Herschel Reference Survey and the JCMT Nearby Galaxies Survey. This review
also discusses the prospects for higher redshifts surveys, including strong
gravitational lens clusters and the AKARI NEP field.Comment: Accepted for Publications of the Korean Astronomical Society
(September 30, 2012 issue, volume 27, No. 3), Proceedings of the Second AKARI
conference, Legacy of AKARI: A Panoramic View of the Dusty Universe. 6 page
Recommended from our members
The <i>AKARI</i> deep fields: early results from multi-wavelength follow-up campaigns
We present early results from our multi-wavelength follow-up campaigns of the AKARI Deep Fields at the North and South Ecliptic Poles. We summarize our campaigns in this poster paper, and present three early outcomes. (a) Our AAOmega optical spectroscopy of the Deep Field South at the AAT has observed over 550 different targets, and our preliminary local luminosity function at 90 ?m from the first four hours of data is in good agreement with the predictions from Serjeant & Harrison (2005). (b) Our GMRT 610 MHz imaging in the Deep Field North has reached ?30 ?Jy RMS, making this among the deepest images at this frequency. Our 610 MHz source counts at >200 ?Jy are the deepest ever derived at this frequency. (c) Comparing our GMRT data with our 1.4 GHz WSRT data, we have found two examples of radio-loud AGN that may have more than one epoch of activity
The ELAIS deep X-ray survey - I. Chandra source catalogue and first results
We present an analysis of two deep (75 ks) Chandra observations of the European Large Area Infrared Space Observatory (ISO) Survey (ELAIS) fields N1 and N2 as the first results from the ELAIS deep X-ray survey. This survey is being conducted in well-studied regions with extensive multiwavelength coverage. Here we present the Chandra source catalogues along with an analysis of source counts, hardness ratios and optical classifications. A total of 233 X-ray point sources are detected in addition to two soft extended sources, which are found to be associated with galaxy clusters. An overdensity of sources is found in N1 with 30 per cent more sources than N2, which we attribute to large-scale structure. A similar variance is seen between other deep Chandra surveys. The source count statistics reveal an increasing fraction of hard sources at fainter fluxes. The number of galaxy-like counterparts also increases dramatically towards fainter fluxes, consistent with the emergence of a large population of obscured sources
Unveiling Dust-enshrouded Star Formation in the Early Universe: a Sub-mm Survey of the Hubble Deep Field
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the faintest optical images are insensitive. We
present the deepest sub-mm survey of the sky to date, taken with the SCUBA
camera on the James Clerk Maxwell Telescope and centred on the Hubble Deep
Field. The high source density found in this image implies that the survey is
confusion-limited below a flux density of 2 mJy. However, within the central 80
arcsec radius independent analyses yield 5 reproducible sources with S(850um) >
2 mJy which simulations indicate can be ascribed to individual galaxies. We
give positions and flux densities for these, and furthermore show using
multi-frequency photometric data that the brightest sources in our map lie at
redshifts z~3. These results lead to integral source counts which are
completely inconsistent with a no-evolution model, and imply that massive
star-formation activity continues at redshifts > 2. The combined brightness of
the 5 most secure sources in our map is sufficient to account for 30 - 50% of
the previously unresolved sub-mm background, and we estimate statistically that
the entire background is resolved at about the 0.3 mJy level. Finally we
discuss possible optical identifications and redshift estimates for the
brightest sources. One source appears to be associated with an extreme
starburst galaxy at z~1, whilst the remaining four appear to lie in the
redshift range 2 < z < 4. This implies a star-formation density over this
redshift range that is at least five times higher than that inferred from the
ultraviolet output of HDF galaxies.Comment: 19 pages, 6 figures (to appear as a Nature Article
A Submillimetre Survey of the Hubble Deep Field: Unveiling Dust-Enshrouded Star Formation in the Early Universe
The advent of sensitive sub-mm array cameras now allows a proper census of
dust-enshrouded massive star-formation in very distant galaxies, previously
hidden activity to which even the deepest optical images are insensitive. We
present the deepest sub-mm survey, taken with the SCUBA camera on the James
Clerk Maxwell Telescope (JCMT) and centred on the Hubble Deep Field (HDF). The
high source density on this image implies that the survey is confusion-limited
below a flux density of 2 mJy. However within the central 80 arcsec radius
independent analyses yield 5 reproducible sources with S(850um) > 2 mJy which
simulations indicate can be ascribed to individual galaxies. These data lead to
integral source counts which are completely inconsistent with a no evolution
model, whilst the combined brightness of the 5 most secure sources in our map
is sufficient to account for 30-50% of the previously unresolved sub-mm
background, and statistically the entire background is resolved at about the
0.3 mJy level. Four of the five brightest sources appear to be associated with
galaxies which lie in the redshift range 2 < z < 4. With the caveat that this
is a small sample of sources detected in a small survey area, these submm data
imply a star-formation density over this redshift range that is at least five
times higher than that inferred from the rest-frame ultraviolet output of HDF
galaxies.Comment: to appear in the proceedings of `The Birth of Galaxies', Xth
Rencontres de Blois, 4 pages, 1 postscript figure, uses blois.sty (included
The ELAIS Deep X-ray Survey
We present initial follow-up results of the ELAIS Deep X-ray Survey which is
being undertaken with the Chandra and XMM-Newton Observatories. 235 X-ray
sources are detected in our two 75 ks ACIS-I observations in the well-studied
ELAIS N1 and N2 areas. 90% of the X-ray sources are identified optically to
R=26 with a median magnitude of R=24. We show that objects which are unresolved
optically (i.e. quasars) follow a correlation between their optical and X-ray
fluxes, whereas galaxies do not. We also find that the quasars with fainter
optical counterparts have harder X-ray spectra, consistent with absorption at
both wavebands. Initial spectroscopic follow-up has revealed a large fraction
of high-luminosity Type 2 quasars. The prospects for studying the evolution of
the host galaxies of X-ray selected Type 2 AGN are considered.Comment: 9 pages, 5 figures, To appear in Proceedings of XXI Moriond
Conference: "Galaxy Clusters and the High Redshift Universe Observed in
X-rays", edited by D. Neumann, F.Durret, & J. Tran Thanh Va
Observations of the Hubble Deep Field South with the Infrared Space Observatory - II. Associations and star formation rates
We present results from a deep mid-IR survey of the Hubble Deep Field South
(HDF-S) region performed at 7 and 15um with the CAM instrument on board ISO. We
found reliable optical/near-IR associations for 32 of the 35 sources detected
in this field by Oliver et al. (2002, Paper I): eight of them were identified
as stars, one is definitely an AGN, a second seems likely to be an AGN, too,
while the remaining 22 appear to be normal spiral or starburst galaxies. Using
model spectral energy distributions (SEDs) of similar galaxies, we compare
methods for estimating the star formation rates (SFRs) in these objects,
finding that an estimator based on integrated (3-1000um) IR luminosity
reproduces the model SFRs best. Applying this estimator to model fits to the
SEDs of our 22 spiral and starburst galaxies, we find that they are forming
stars at rates of ~1-100 M_sol/yr, with a median value of ~40M_sol/yr, assuming
an Einstein - de Sitter universe with a Hubble constant of 50 km/s/Mpc, and
star formation taking place according to a Salpeter (1955) IMF across the mass
range 0.1-100M_sol. We split the redshift range 0.0<z<0.6 into two equal-volume
bins to compute raw estimates of the star formation rate density contributed by
these sources, assuming the same cosmology and IMF as above and computing
errors based on estimated uncertainties in the SFRs of individual galaxies. We
compare these results with other estimates of the SFR density made with the
same assumptions, showing them to be consistent with the results of Flores et
al. (1999) from their ISO survey of the CFRS 1415+52 field. However, the
relatively small volume of our survey means that our SFR density estimates
suffer from a large sampling variance, implying that our results, by
themselves, do not place tight constraints on the global mean SFR density.Comment: Accepted for MNRAS. 23 pages, 10 figures (Figs. 4&6 included here as
low resolution JPEGS), latex, uses mn,epsfig. Further information and full
resolution versions of Figs 4&6 available at http://astro.ic.ac.uk/hdfs (v2:
full author list added
A spectroscopic study of IRAS F10214+4724
The z=2.286 IRAS galaxy F10214+4724 remains one of the most luminous galaxies
in the Universe, despite its gravitational lens magnification. We present
optical and near-infrared spectra of F10214+4724, with clear evidence for three
distinct components: lines of width ~1000 km/s from a Seyfert-II nucleus; <~200
km/s lines which are likely to be associated with star formation; and a broad
~4000 km/s CIII] 1909ang emission line which is blue-shifted by ~1000 km/s with
respect to the Seyfert-II lines. Our study of the Seyfert-II component leads to
several new results, including: (i) From the double-peaked structure in the Ly
alpha line, and the lack of Ly beta, we argue that the Ly alpha photons have
emerged through a neutral column of N_H ~ 2.5 x 10^{25}/m^2, possibly located
within the AGN narrow-line region as argued in several high redshift
radiogalaxies. (ii) The resonant O VI 1032,1036ang doublet (previously
identified as Ly beta) is in an optically thick (1:1) ratio. At face value this
implies an an extreme density (n_e ~ 10^{17}/m^3) more typical of broad line
region clouds. However, we attribute this instead to the damping wings of Ly
beta from the resonant absorption. (iii) A tentative detection of HeII 1086
suggests little extinction in the rest-frame ultraviolet.Comment: Accepted for publication in MNRAS. Uses BoxedEPS (included
Photometric redshift accuracy in AKARI Deep Surveys
We investigate the photometric redshift accuracy achievable with the AKARI
infrared data in deep multi-band surveys, such as in the North Ecliptic Pole
field. We demonstrate that the passage of redshifted policyclic aromatic
hydrocarbons and silicate features into the mid-infrared wavelength window
covered by AKARI is a valuable means to recover the redshifts of starburst
galaxies. To this end we have collected a sample of ~60 galaxies drawn from the
GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry
from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The
infrared spectra are fitted using synthetic galaxy Spectral Energy
Distributions which account for starburst and active nuclei emission. For ~90%
of the sources in our sample the redshift is recovered with an accuracy
|z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets
of simulated spectra shows that the AKARI infrared data alone can provide
photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) at
z<~2. At higher redshifts the PAH features are shifted outside the wavelength
range covered by AKARI and the photo-z estimates rely on the less prominent 1.6
micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%,
provided that the AGN contribution to the infrared emission is subdominant. Our
technique is no more prone to redshift aliasing than optical-uv photo-z, and it
may be possible to reduce this aliasing further with the addition of
submillimetre and/or radio data.Comment: 27 pages, 12 figures, 4 tables. Accepted for publication on MNRA
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