Abstract
The Euclid telescope, due for launch in 2021, will perform an imaging and slitless spectroscopy survey over half the sky, to map baryon wiggles and weak lensing. During the survey, Euclid is ...expected to resolve 100 000 strong gravitational lens systems. This is ideal to find rare lens configurations, provided they can be identified reliably and on a reasonable time-scale. For this reason, we have developed a convolutional neural network (CNN) that can be used to identify images containing lensing systems. CNNs have already been used for image and digit classification as well as being used in astronomy for star-galaxy classification. Here, our CNN is trained and tested on Euclid-like and KiDS (Kilo-Degree Survey)-like simulations from the Euclid Strong Lensing Group, successfully classifying 77 per cent of lenses, with an area under the ROC curve of up to 0.96. Our CNN also attempts to classify the lenses in COSMOS Hubble Space Telescope F814W-band images. After convolution to the Euclid resolution, we find we can recover most systems that are identifiable by eye. The python code is available on Github.
ABSTRACT
The JWST has discovered a surprising abundance of bright galaxy candidates in the very early universe (≤500 Myr after the Big Bang), calling into question current galaxy formation models. ...Spectroscopy is needed to confirm the primeval nature of these candidates, as well as to understand how the first galaxies form stars and grow. Here we present deep spectroscopic and continuum ALMA observations towards GHZ2/GLASS-z12, one of the brightest and most robust candidates at z > 10, identified in the GLASS-JWST Early Release Science Program. We detect a 5.8σ line, offset 0${_{.}^{\prime\prime}}$5 from the JWST position of GHZ2/GLASS-z12, that associating it with the O iii 88 $\mu {\rm m}$ transition, implies a spectroscopic redshift of z = 12.117 ± 0.001. We verify the detection using extensive statistical tests. The oxygen line luminosity places GHZ2/GLASS-z12 above the O iii-SFR relation for metal-poor galaxies, implying an enhancement of O iii emission in this system while the JWST-observed emission is likely a lower-metallicity region. The lack of dust emission seen by these observations is consistent with the blue UV slope observed by JWST, which suggest little dust attenuation in galaxies at this early epoch. Further observations will unambiguously confirm the redshift and shed light on the origins of the wide and offset line and physical properties of this early galaxy. This work illustrates the synergy between JWST and ALMA, and paves the way for future spectroscopic surveys of z > 10 galaxy candidates.
Abstract
Bright submillimetre-selected galaxies have been found to be a rich source of strong gravitational lenses. However, strong gravitational lensing of extended sources leads inevitably to ...differential magnification. In this paper I quantify the effect of differential magnification on simulated far-infrared and submillimetre surveys of strong gravitational lenses, using a foreground population of Navarro-Frenk-White plus de Vaucouleurs' density profiles, with a model source resembling the Cosmic Eyelash and quasi-stellar object J1148+5251. Some emission-line diagnostics are surprisingly unaffected by differential magnification effects: for example, the bolometric fractions of Cii 158 μm and CO(J = 1 − 0), often used to infer densities and ionization parameters, have typical differential magnification effects that are smaller than the measurement errors. However, the CO ladder itself is significantly affected. Far-infrared lensed galaxy surveys (e.g. at 60 μm) strongly select for high-redshift galaxies with caustics close to active galactic nuclei (AGNs), boosting the apparent bolometric contribution of AGN. The lens configuration of IRAS F10214+4724 is naturally explained in this context. Conversely, submillimetre/millimetre-wave surveys (e.g. 500-1400 μm) strongly select for caustics close to knots of star formation boosting the latter's bolometric fraction. In general, estimates of bolometric fractions from spectral energy distributions of strongly lensed infrared galaxies are so unreliable as to be useless, unless a lens mass model is available to correct for differential magnification.
ABSTRACT We present the rest-frame optical spectral properties of 155 luminous quasars at 3.3 < z < 6.4 taken with the AKARI space telescope, including the first detection of the H emission line as ...far out as z ∼ 6. We extend the scaling relation between the rest-frame optical continuum and the line luminosity of active galactic nuclei (AGNs) to the high-luminosity, high-redshift regime that has rarely been probed before. Remarkably, we find that a single log-linear relation can be applied to the 5100 and H AGN luminosities over a wide range of luminosity (1042 < < 1047 ergs s−1) or redshift (0 < z < 6), suggesting that the physical mechanism governing this relation is unchanged from z = 0 to 6, over five decades in luminosity. Similar scaling relations are found between the optical and the UV continuum luminosities or line widths. Applying the scaling relations to the Hβ black hole (BH) mass ( ) estimator of local AGNs, we derive the estimators based on the H , Mg ii, and C iv lines, finding that the UV-line-based masses are overall consistent with the Balmer-line-based, but with a large intrinsic scatter of 0.40 dex for the C iv estimates. Our 43 estimates from H confirm the existence of BHs as massive as ∼ out to z ∼ 5 and provide a secure footing for previous results from Mg ii-line-based studies that a rapid growth has occurred in the early universe.
Abstract
We introduce an ALMA band 3 spectroscopic survey targeting the brightest submillimeter galaxies (SMGs) in the COSMOS field. Here we present the first results based on the 18 primary SMGs ...that have 870
μ
m flux densities of
S
870
= 12.4–19.3 mJy and are drawn from a parent sample of 260 ALMA-detected SMGs from the AS2COSMOS survey. We detect emission lines in 17 and determine their redshifts to be in the range of
z
= 2–5 with a median of 3.3 ± 0.3. We confirm that SMGs with brighter
S
870
are located at higher redshifts. The data additionally cover five fainter companion SMGs, and we obtain line detection in one. Together with previous studies, our results indicate that for SMGs that satisfy our selection, their brightest companion SMGs are physically associated with their corresponding primary SMGs ≥40% of the time, suggesting that mergers play a role in the triggering of star formation. By modeling the foreground gravitational fields, <10% of the primary SMGs can be strongly lensed with a magnification
μ
> 2. We determine that about 90% of the primary SMGs have lines that are better described by double Gaussian profiles, and the median separation of the two Gaussian peaks is 430 ± 40 km s
−1
. This allows estimates of an average baryon mass, which, together with the line dispersion measurements, puts our primary SMGs on the similar mass–
σ
correlation found on local early-type galaxies. Finally, the number density of our
z
> 4 primary SMGs is found to be
1
−
0.6
+
0.9
×
10
−
6
cMpc
−3
, suggesting that they can be the progenitors of
z
∼ 3−4 massive quiescent galaxies.
Abstract
We report the physical properties of the 18 brightest (
S
870
μ
m
= 12.4–19.2 mJy) and not strongly lensed 870
μ
m–selected dusty star-forming galaxies (DSFGs), also known as submillimeter ...galaxies (SMGs), in the COSMOS field. This sample is part of an ALMA band 3 spectroscopic survey (AS2COSPEC), and spectroscopic redshifts are measured in 17 of them at
z
= 2–5. We perform spectral energy distribution analyses and deduce a median total infrared luminosity of
L
IR
= (1.3 ± 0.1) × 10
13
L
⊙
, infrared-based star formation rate (SFR) of SFR
IR
= 1390 ± 150
M
⊙
yr
−1
, stellar mass of
M
*
= (1.4 ± 0.6) × 10
11
M
⊙
, dust mass of
M
dust
= (3.7 ± 0.5) × 10
9
M
⊙
, and molecular gas mass of
M
gas
= (
α
CO
/0.8)(1.2 ± 0.1) × 10
11
M
⊙
, suggesting that they are one of the most massive, ISM-enriched, and actively star-forming systems at
z
= 2–5. In addition, compared to less massive and less active galaxies at similar epochs, SMGs have comparable gas fractions; however, they have a much shorter depletion time, possibly caused by more active dynamical interactions. We determine a median dust emissivity index of
β
= 2.1 ± 0.1 for our sample, and by combining our results with those from other DSFG samples, we find no correlation of
β
with redshift or infrared luminosity, indicating similar dust grain compositions across cosmic time for infrared luminous galaxies. We also find that AS2COSPEC SMGs have one of the highest dust-to-stellar mass ratios, with a median of 0.02 ± 0.01, significantly higher than model predictions, possibly due to too-strong active galactic nucleus feedback implemented in the model. Finally, our complete and uniform survey enables us to put constraints on the most massive end of the dust and molecular gas mass functions.
ABSTRACT
To understand the cosmic accretion history of supermassive black holes, separating the radiation from active galactic nuclei (AGNs) and star-forming galaxies (SFGs) is critical. However, a ...reliable solution on photometrically recognizing AGNs still remains unsolved. In this work, we present a novel AGN recognition method based on Deep Neural Network (Neural Net; NN). The main goals of this work are (i) to test if the AGN recognition problem in the North Ecliptic Pole Wide (NEPW) field could be solved by NN; (ii) to show that NN exhibits an improvement in the performance compared with the traditional, standard spectral energy distribution (SED) fitting method in our testing samples; and (iii) to publicly release a reliable AGN/SFG catalogue to the astronomical community using the best available NEPW data, and propose a better method that helps future researchers plan an advanced NEPW data base. Finally, according to our experimental result, the NN recognition accuracy is around 80.29 per cent–85.15 per cent, with AGN completeness around 85.42 per cent–88.53 per cent and SFG completeness around 81.17 per cent–85.09 per cent.
Abstract We present confusion-limited SCUBA-2 450 μ m observations in the COSMOS-CANDELS region as part of the James Clerk Maxwell Telescope Large Program SCUBA-2 Ultra Deep Imaging EAO Survey. Our ...maps at 450 and 850 μ m cover an area of 450 arcmin 2 . We achieved instrumental noise levels of σ 450 = 0.59 mJy beam −1 and σ 850 = 0.09 mJy beam −1 in the deepest area of each map. The corresponding confusion noise levels are estimated to be 0.65 and 0.36 mJy beam −1 . Above the 4 σ (3.5 σ ) threshold, we detected 360 (479) sources at 450 μ m and 237 (314) sources at 850 μ m. We derive the deepest blank-field number counts at 450 μ m, covering the flux-density range of 2–43 mJy. These are in agreement with other SCUBA-2 blank-field and lensing-cluster observations but are lower than various model counts. We compare the counts with those in other fields and find that the field-to-field variance observed at 450 μ m at the R = 6 ′ scale is consistent with Poisson noise, so there is no evidence of strong 2D clustering at this scale. Additionally, we derive the integrated surface brightness at 450 μ m down to 2.1 mJy to be 57.3 − 6.2 + 1.0 Jy deg −2 , contributing to 41% ± 4% of the 450 μ m extragalactic background light (EBL) measured by Cosmic Background Explorer and Planck. Our results suggest that the 450 μ m EBL may be fully resolved at 0.08 − 0.08 + 0.09 mJy, which extremely deep lensing-cluster observations and next-generation submillimeter instruments with large aperture sizes may be able to achieve.
ABSTRACT
Galaxy clusters provide an excellent probe in various research fields in astrophysics and cosmology. However, the number of galaxy clusters detected so far in the AKARI North Ecliptic Pole ...(NEP) field is limited. In this work, we provide galaxy cluster candidates in the AKARI NEP field with the minimum requisites based only on the coordinates and photometric redshift (photo-z) of galaxies. We used galaxies detected in five optical bands (g, r, i, z, and Y) by the Subaru Hyper Suprime-Cam (HSC), with additional data from the u band obtained from the Canada-France-Hawaii Telescope (CFHT) MegaPrime/MegaCam, and from the IRAC1 and IRAC2 bands from the Spitzer space telescope for photo-z estimation. We calculated the local density around every galaxy using the 10th-nearest neighbourhood. Cluster candidates were determined by applying the friends-of-friends algorithm to over-densities. A total of 88 cluster candidates containing 4390 member galaxies below redshift 1.1 in 5.4 deg2 were identified. The reliability of our method was examined through false-detection tests, redshift-uncertainty tests, and applications on the Cosmic Evolution Survey (COSMOS) data, giving false-detection rates of 0.01 to 0.05 and a recovery rate of 0.9 at high richness. Three X-ray clusters previously observed by ROSAT and Chandra were recovered. The cluster galaxies show a higher stellar mass and lower star formation rate compared with the field galaxies in two-sample Z-tests. These cluster candidates are useful for environmental studies of galaxy evolution and future astronomical surveys in the NEP, where AKARI has performed unique nine-band mid-infrared photometry for tens of thousands of galaxies.
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