147 research outputs found
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments
carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on
2000 October 9. HETE-2 is an international mission consisting of a small
satellite dedicated to provide broad-band observations and accurate
localizations of gamma-ray bursts (GRBs). A unique feature of this mission is
its capability to determine and transmit GRB coordinates in almost real-time
through the burst alert network. The WXM consists of three elements: four
identical Xe-filled one-dimensional position-sensitive proportional counters,
two sets of one-dimensional coded apertures, and the main electronics. The WXM
counters are sensitive to X-rays between 2 keV and 25 keV within a
field-of-view of about 1.5 sr, with a total detector area of about 350 cm.
The in-flight triggering and localization capability can produce a real-time
GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
erg cm. In this report, the details of the mechanical
structure, electronics, on-board software, ground and in-flight calibration,
and in-flight performance of the WXM are discussed.Comment: 28 pages, 24 figure
AzTEC/ASTE 1.1-mm Survey of the AKARI Deep Field South: source catalogue and number counts
We present results of a 1.1 mm deep survey of the AKARI Deep Field South
(ADF-S) with AzTEC mounted on the Atacama Submillimetre Telescope Experiment
(ASTE). We obtained a map of 0.25 sq. deg area with an rms noise level of
0.32-0.71 mJy. This is one of the deepest and widest maps thus far at
millimetre and submillimetre wavelengths. We uncovered 198 sources with a
significance of 3.5-15.6 sigma, providing the largest catalog of 1.1 mm sources
in a contiguous region. Most of the sources are not detected in the
far-infrared bands of the AKARI satellite, suggesting that they are mostly at z
~ 1.5 given the detection limits. We constructed differential and cumulative
number counts in the ADF-S, the Subaru/XMM Newton Deep Field (SXDF), and the
SSA 22 field surveyed by AzTEC/ASTE, which provide currently the tightest
constraints on the faint end. The integration of the best-fit number counts in
the ADF-S find that the contribution of 1.1 mm sources with fluxes >=1 mJy to
the cosmic infrared background (CIB) at 1.1 mm is 12-16%, suggesting that the
large fraction of the CIB originates from faint sources of which the number
counts are not yet constrained. We estimate the cosmic star-formation rate
density contributed by 1.1 mm sources with >=1 mJy using the best-fit number
counts in the ADF-S and find that it is lower by about a factor of 5-10
compared to those derived from UV/optically-selected galaxies at z ~ 2-3. The
fraction of stellar mass of the present-day universe produced by 1.1 mm sources
with >=1 mJy at z >= 1 is ~20%, calculated by the time integration of the
star-formation rate density. If we consider the recycled fraction of >0.4,
which is the fraction of materials forming stars returned to the interstellar
medium, the fraction of stellar mass produced by 1.1 mm sources decrease to
<~10%.Comment: 15 pages, 12 figure, accepted for publication in MNRA
SXDF-UDS-CANDELS-ALMA 1.5 arcmin deep survey
We have conducted 1.1 mm ALMA observations of a contiguous or 1.5 arcmin window in the SXDF-UDS-CANDELS. We achieved a 5
sensitivity of 0.28 mJy, providing a flat sensus of dusty star-forming galaxies
with (for =40K) up to
thanks to the negative K-correction at this wavelength. We detected 5
brightest sources (S/N6) and 18 low-significance sources (5S/N4; these
may contain spurious detections, though). One of the 5 brightest ALMA sources
( mJy) is extremely faint in the WFC3 and
VLT/HAWK-I images, demonstrating that a contiguous ALMA imaging survey is able
to uncover a faint dust-obscured population that is invisible in deep
optical/near-infrared surveys. We found a possible [CII]-line emitter at
or a low- CO emitting galaxy within the field, which may allow us
to constrain the [CII] and/or the CO luminosity functions across the history of
the universe.Comment: 4 pages, 2 figures, 1 table, to appear in the proceedings of IAU
Symposium 319 "Galaxies at High Redshift and Their Evolution over Cosmic
Time", eds. S. Kaviraj & H. Ferguso
AzTEC 1.1 mm observations of high-z protocluster environments : SMG overdensities and misalignment between AGN jets and SMG distribution
We present observations at 1.1 mm towards 16 powerful radio galaxies and a radio-quiet quasar at 0.5 > z > 6.3 acquired with the AzTEC camera mounted at the James Clerk Maxwell Telescope and Atacama Submillimeter Telescope Experiment to study the spatial distribution of submillimetre galaxies (SMGs) towards possible protocluster regions. The survey covers a total area of 1.01 sq deg with rms depths of 0.52-1.44 mJy and detects 728 sources above 3σ. We find overdensities of a factor of ~2 in the source counts of three individual fields (4C+23.56, PKS1138-262, and MRC0355-037) over areas of ~200 sq deg. When combining all fields, the source-count analysis finds an overdensity that reaches a factor ≳ 3 at S 1.1mm = 4mJy covering a 1.5-arcmin-radius area centred on the active galactic nucleus. The large size of our maps allows us to establish that beyond a radius of 1.5 arcmin, the radial surface density of SMGs falls to that of a blank field. In addition, we find a trend for SMGs to align closely to a perpendicular direction with respect to the radio jets of the powerful central radio galaxies (73 -14 +13 deg). This misalignment is found over projected comoving scales of 4-20 Mpc, departs from perfect alignment (0 deg) by ~5σ, and apparently has no dependence on SMG luminosity. Under the assumption that the AzTEC sources are at the redshift of the central radio galaxy, the misalignment reported here can be interpreted as SMGs preferentially inhabiting mass-dominant filaments funnelling material towards the protoclusters, which are also the parent structures of the radio galaxies.Peer reviewe
Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE -- II. Redshift distribution and nature of the submillimetre galaxy population
We report the results of the counterpart identification and a detailed
analysis of the physical properties of the 48 sources discovered in our deep
1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC
instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or
more robust or tentative counterpart candidate is found for 27 and 14 AzTEC
sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC,
and LABOCA 870 micron data. Five of the sources (10%) have two robust
counterparts each, supporting the idea that these galaxies are strongly
clustered and/or heavily confused. Photometric redshifts and star formation
rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The
median redshift of z~2.6 is similar to other earlier estimates, but we show
that 80% of the AzTEC-GOODS sources are at z>2, with a significant high
redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC
sources are extremely diverse, spanning 10 magnitude in the i- and K-band
photometry with median values of i=25.3 and K=22.6 and a broad range of red
colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in
the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x
10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000
solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is
independent of redshift or stellar mass. The resulting specific star formation
rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies
at z=0, and they extend the previously observed rapid rise in the SSFR with
redshift to z=2-5. These galaxies have a SFR high enough to have built up their
entire stellar mass within their Hubble time. We find only marginal evidence
for an AGN contribution to the near-IR and mid-IR SEDs. (abridged)Comment: 31 pages including 14 figures, accepted for publication in the MNRAS.
A higher quality Figure 1 is also included as Figure1.jp
AzTEC millimeter survey of the COSMOS field - III. Source catalog over 0.72 sq. deg. and plausible boosting by large-scale structure
We present a 0.72 sq. deg. contiguous 1.1mm survey in the central area of the
COSMOS field carried out to a 1sigma ~ 1.26 mJy/beam depth with the AzTEC
camera mounted on the 10m Atacama Submillimeter Telescope Experiment (ASTE). We
have uncovered 189 candidate sources at a signal-to-noise ratio S/N >= 3.5, out
of which 129, with S/N >= 4, can be considered to have little chance of being
spurious (< 2 per cent). We present the number counts derived with this survey,
which show a significant excess of sources when compared to the number counts
derived from the ~0.5 sq. deg. area sampled at similar depths in the Scuba HAlf
Degree Extragalactic Survey (SHADES, Austermann et al. 2010). They are,
however, consistent with those derived from fields that were considered too
small to characterize the overall blank-field population. We identify
differences to be more significant in the S > 5 mJy regime, and demonstrate
that these excesses in number counts are related to the areas where galaxies at
redshifts z < 1.1 are more densely clustered. The positions of optical-IR
galaxies in the redshift interval 0.6 < z < 0.75 are the ones that show the
strongest correlation with the positions of the 1.1mm bright population (S > 5
mJy), a result which does not depend exclusively on the presence of rich
clusters within the survey sampled area. The most likely explanation for the
observed excess in number counts at 1.1mm is galaxy-galaxy and galaxy-group
lensing at moderate amplification levels, that increases in amplitude as one
samples larger and larger flux densities. This effect should also be detectable
in other high redshift populations.Comment: 21 pages, 17 figures, accepted for publication in MNRA
SXDF-ALMA 1.5 arcmin^2 deep survey. A compact dusty star-forming galaxy at z=2.5
We present first results from the SXDF-ALMA 1.5 arcmin^2 deep survey at 1.1
mm using Atacama Large Millimeter Array (ALMA). The map reaches a 1sigma depth
of 55 uJy/beam and covers 12 Halpha-selected star-forming galaxies at z = 2.19
or z=2.53. We have detected continuum emission from three of our
Halpha-selected sample, including one compact star-forming galaxy with high
stellar surface density, NB2315-07. They are all red in the rest-frame optical
and have stellar masses of log (M*/Msun)>10.9 whereas the other blue,
main-sequence galaxies with log(M*/Msun)=10.0-10.8 are exceedingly faint, <290
uJy (2sigma upper limit). We also find the 1.1 mm-brightest galaxy, NB2315-02,
to be associated with a compact (R_e=0.7+-0.1 kpc), dusty star-forming
component. Given high gas fraction (44^{+20}_{-8}% or 37^{+25}_{-3}%) and high
star formation rate surface density (126^{+27}_{-30} Msun yr^{-1}kpc^{-2}), the
concentrated starburst can within less than 50^{+12}_{-11} Myr build up a
stellar surface density matching that of massive compact galaxies at z~2,
provided at least 19+-3% of the total gas is converted into stars in the galaxy
centre. On the other hand, NB2315-07, which already has such a high stellar
surface density core, shows a gas fraction (23+-8%) and is located in the lower
envelope of the star formation main-sequence. This compact less star-forming
galaxy is likely to be in an intermediate phase between compact dusty
star-forming and quiescent galaxies.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ
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