27 research outputs found
Testing strong line metallicity diagnostics at z~2
High-z galaxy gas-phase metallicities are usually determined through
observations of strong optical emission lines with calibrations tied to the
local universe. Recent debate has questioned if these calibrations are valid in
the high-z universe. We investigate this by analysing a sample of 16 galaxies
at z~2 available in the literature, and for which the metallicity can be
robustly determined using oxygen auroral lines. The sample spans a redshift
range of 1.4 < z < 3.6, has metallicities of 7.4-8.4 in 12+log(O/H) and stellar
masses 10^7.5-10^11 Msun. We test commonly used strong line diagnostics (R23,
O3, O2, O32, N2, O3N2 and Ne3O2 ) as prescribed by four different sets of
empirical calibrations, as well as one fully theoretical calibration. We find
that none of the strong line diagnostics (or calibration set) tested perform
consistently better than the others. Amongst the line ratios tested, R23 and O3
deliver the best results, with accuracies as good as 0.01-0.04 dex and
dispersions of ~0.2 dex in two of the calibrations tested. Generally, line
ratios involving nitrogen predict higher values of metallicity, while results
with O32 and Ne3O2 show large dispersions. The theoretical calibration yields
an accuracy of 0.06 dex, comparable to the best strong line methods. We
conclude that, within the metallicity range tested in this work, the locally
calibrated diagnostics can still be reliably applied at z~2.Comment: 12 pages, 8 Figures, accepted for publication in MNRA
HOLISMOKES -- IX. Neural network inference of strong-lens parameters and uncertainties from ground-based images
Modeling of strong gravitational lenses is a necessity for further
applications in astrophysics and cosmology. Especially with the large number of
detections in current and upcoming surveys such as the Rubin Legacy Survey of
Space and Time (LSST), it is timely to investigate in automated and fast
analysis techniques beyond the traditional and time consuming Markov chain
Monte Carlo sampling methods. Building upon our convolutional neural network
(CNN) presented in Schuldt et al. (2021b), we present here another CNN,
specifically a residual neural network (ResNet), that predicts the five mass
parameters of a Singular Isothermal Ellipsoid (SIE) profile (lens center
and , ellipticity and , Einstein radius ) and the
external shear (, ) from ground-based imaging
data. In contrast to our CNN, this ResNet further predicts a 1
uncertainty for each parameter. To train our network, we use our improved
pipeline from Schuldt et al. (2021b) to simulate lens images using real images
of galaxies from the Hyper Suprime-Cam Survey (HSC) and from the Hubble Ultra
Deep Field as lens galaxies and background sources, respectively. We find
overall very good recoveries for the SIE parameters, while differences remain
in predicting the external shear. From our tests, most likely the low image
resolution is the limiting factor for predicting the external shear. Given the
run time of milli-seconds per system, our network is perfectly suited to
predict the next appearing image and time delays of lensed transients in time.
Therefore, we also present the performance of the network on these quantities
in comparison to our simulations. Our ResNet is able to predict the SIE and
shear parameter values in fractions of a second on a single CPU such that we
are able to process efficiently the huge amount of expected galaxy-scale lenses
in the near future.Comment: 16 pages, including 11 figures, accepted for publication by A&
HOLISMOKES -- IV. Efficient mass modeling of strong lenses through deep learning
Modelling the mass distributions of strong gravitational lenses is often
necessary to use them as astrophysical and cosmological probes. With the high
number of lens systems () expected from upcoming surveys, it is timely
to explore efficient modeling approaches beyond traditional MCMC techniques
that are time consuming. We train a CNN on images of galaxy-scale lenses to
predict the parameters of the SIE mass model (, and ).
To train the network, we simulate images based on real observations from the
HSC Survey for the lens galaxies and from the HUDF as lensed galaxies. We
tested different network architectures, the effect of different data sets, and
using different input distributions of . We find that the CNN
performs well and obtain with the network trained with a uniform distribution
of the following median values with scatter:
, ,
,
and . The bias in is driven by
systems with small . Therefore, when we further predict the multiple
lensed image positions and time delays based on the network output, we apply
the network to the sample limited to . In this case, the offset
between the predicted and input lensed image positions is
and for and ,
respectively. For the fractional difference between the predicted and true time
delay, we obtain . Our CNN is able to predict the SIE
parameters in fractions of a second on a single CPU and with the output we can
predict the image positions and time delays in an automated way, such that we
are able to process efficiently the huge amount of expected lens detections in
the near future.Comment: 17 pages, 14 Figure
Constraining the multi-scale dark-matter distribution in CASSOWARY 31 with strong gravitational lensing and stellar dynamics
We study the inner structure of the group-scale lens CASSOWARY 31 (CSWA 31)
by adopting both strong lensing and dynamical modeling. CSWA 31 is a peculiar
lens system. The brightest group galaxy (BGG) is an ultra-massive elliptical
galaxy at z = 0.683 with a weighted mean velocity dispersion of km s. It is surrounded by group members and several lensed arcs
probing up to ~150 kpc in projection. Our results significantly improve
previous analyses of CSWA 31 thanks to the new HST imaging and MUSE
integral-field spectroscopy. From the secure identification of five sets of
multiple images and measurements of the spatially-resolved stellar kinematics
of the BGG, we conduct a detailed analysis of the multi-scale mass distribution
using various modeling approaches, both in the single and multiple lens-plane
scenarios. Our best-fit mass models reproduce the positions of multiple images
and provide robust reconstructions for two background galaxies at z = 1.4869
and z = 2.763. The relative contributions from the BGG and group-scale halo are
remarkably consistent in our three reference models, demonstrating the
self-consistency between strong lensing analyses based on image position and
extended image modeling. We find that the ultra-massive BGG dominates the
projected total mass profiles within 20 kpc, while the group-scale halo
dominates at larger radii. The total projected mass enclosed within =
27.2 kpc is M. We find that CSWA
31 is a peculiar fossil group, strongly dark-matter dominated towards the
central region, and with a projected total mass profile similar to higher-mass
cluster-scale halos. The total mass-density slope within the effective radius
is shallower than isothermal, consistent with previous analyses of early-type
galaxies in overdense environments.Comment: 22 pages, 12 figures, 5 tables, submitted to Astronomy &
Astrophysics. We welcome the comments from reader
Planck \u27s Dusty GEMS: VIII. Dense-gas reservoirs in the most active dusty starbursts at z âŒ3
We present ALMA, NOEMA, and IRAM-30 m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at zâČ 3-3.5, part of the Planck\u27s Dusty Gravitationally Enhanced subMillimetre Sources (GEMS), with the aim of probing the gas reservoirs closely associated with their exceptional levels of star formation. We obtained robust detections of ten emission lines between Jup = 4 and 6, as well as several additional upper flux limits. In PLCK_G244.8+54.9, the brightest source at z = 3.0, the HNC(5-4) line emission at 0.1âł resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. This line is blended with CN(4-3) and in this source, we measure a HNC(5-4)/CN(4-3) flux ratio of 1.76 \ub10. 86. Dense-gas line profiles generally match those of mid-J CO lines, except in PLCK_G145.2+50.8, which also has dense-gas line fluxes that are relatively lower, perhaps due to fewer dense cores and more segregated dense and diffuse gas phases in this source. The HCO+/HCN 1 and HNC/HCN ⌠1 line ratios in our sample are similar to those of nearby ultraluminous infrared galaxies (ULIRGs) and consistent with photon-dominated regions without any indication of important mechanical heating or active galactic nuclei feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with an H2 density of n ⌠105-106 cm-3, although important degeneracies hinder a determination of the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z ⌠3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional as compared to other lensed dusty star-forming galaxies at z > 2, and they fall near the upper envelope of local ULIRGs. Despite the higher overall gas fractions and local gas-mass surface densities observed at high redshift, the dense-gas budget of rapidly star-forming galaxies seems to have evolved little between z ⌠3 and z ⌠0. Our results favor constant dense-gas depletion times in these populations, which is in agreement with theoretical models of star formation
The impact of human expert visual inspection on the discovery of strong gravitational lenses
We investigate the ability of human âexpertâ classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25% of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with g-band signal-to-noise less than âŒ25 or Einstein radii less than âŒ1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifierâs experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies
Planckâs dusty GEMS - IV. Star formation and feedback in a maximum starburst at z = 3 seen at 60-pc resolution
International audienceWe present an analysis of high-resolution ALMA interferometry of CO(4â3) line emission and dust continuum in the âRubyâ (PLCK_G244.8+54.9), a bright, gravitationally lensed galaxy at z = 3.0 discovered with the Planck all-sky survey. The Ruby is the brightest of Planckâs dusty GEMS, a sample of 11 of the brightest gravitationally lensed high-redshift galaxies on the extragalactic sub-mm sky. We resolve the high-surface-brightness continuum and CO line emission of the Ruby in several extended clumps along a partial, nearly circular Einstein ring with 1.4âČâČ diameter around a massive galaxy at z = 1.5. Local star-formation intensities are up to 2000 Mââyr-1âkpc-2, amongst the highest observed at high redshift, and clearly in the range of maximal starbursts. Gas-mass surface densities are a few Ă 104Mâ pc-2. The Ruby lies at, and in part even above, the starburst sequence in the Schmidt-Kennicutt diagram, and at the limit expected for star formation that is self-regulated through the kinetic energy injection from radiation pressure, stellar winds, and supernovae. We show that these processes can also inject sufficient kinetic energy and momentum into the gas to explain the turbulent line widths, which are consistent with marginally gravitationally bound molecular clouds embedded in a critically Toomre-stable disk. The star-formation efficiency is in the range 1â10% per free-fall time, consistent with the notion that the pressure balance that sets the local star-formation law in the Milky Way may well be universal out to the highest star-formation intensities. AGN feedback is not necessary to regulate the star formation in the Ruby, in agreement with the absence of a bright AGN component in the infrared and radio regimes.Key words: galaxies: starburst / galaxies: high-redshift / submillimeter: galaxies / galaxies: evolution / galaxies: star formation / galaxies: ISMâ Based on ALMA data obtained with program 2015.1.01518.S
Photometric redshift estimation with a convolutional neural network: NetZ
Galaxy redshifts are a key characteristic for nearly all extragalactic studies. Since spectroscopic redshifts require additional telescope and human resources, millions of galaxies are known without spectroscopic redshifts. Therefore, it is crucial to have methods for estimating the redshift of a galaxy based on its photometric properties, the so-called photo-z. We have developed NetZ, a new method using a convolutional neural network (CNN) to predict the photo-z based on galaxy images, in contrast to previous methods that often used only the integrated photometry of galaxies without their images. We use data from the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) in five different filters as the training data. The network over the whole redshift range between 0 and 4 performs well overall and especially in the high-z range, where it fares better than other methods on the same data. We obtained a precision |zpredâ
ââ
zref| of Ïâ=â0.12 (68% confidence interval) with a CNN working for all galaxy types averaged over all galaxies in the redshift range of 0 to âŒ4. We carried out a comparison with a network trained on point-like sources, highlighting the importance of morphological information for our redshift estimation. By limiting the scope to smaller redshift ranges or to luminous red galaxies, we find a further notable improvement. We have published more than 34 million new photo-z values predicted with NetZ. This shows that the new method is very simple and swift in application, and, importantly, it covers a wide redshift range that is limited only by the available training data. It is broadly applicable, particularly with regard to upcoming surveys such as the Rubin Observatory Legacy Survey of Space and Time, which will provide images of billions of galaxies with similar image quality as HSC. Our HSC photo-z estimates are also beneficial to the Euclid survey, given the overlap in the footprints of the HSC and Euclid
Recommended from our members
Searching for Strong Gravitational Lenses
Acknowledgements: We thank the International Space Science Institute in Bern (ISSI) for their hospitality and the conveners for organizing the stimulating workshop on âStrong Gravitational Lensingâ.Funder: EPFL LausanneAbstractStrong gravitational lenses provide unique laboratories for cosmological and astrophysical investigations, but they must first be discovered â a task that can be met with significant contamination by other astrophysical objects and asterisms. Here we review strong lens searches, covering various sources (quasars, galaxies, supernovae, FRBs, GRBs, and GWs), lenses (early- and late-type galaxies, groups, and clusters), datasets (imaging, spectra, and lightcurves), and wavelengths. We first present the physical characteristics of the lens and source populations, highlighting relevant details for constructing targeted searches. Search techniques are described based on the main lensing feature that is required for the technique to work, namely one of: (i) an associated magnification, (ii) multiple spatially-resolved images, (iii) multiple redshifts, or (iv) a non-zero time delay between images. To use the current lens samples for science, and for the design of future searches, we list several selection biases that exist due to these discovery techniques. We conclude by discussing the future of lens searches in upcoming surveys and the new population of lenses that will be discovered.</jats:p