25 research outputs found
Galaxy Zoo: Kinematics of strongly and weakly barred galaxies
We study the bar pattern speeds and corotation radii of 225 barred galaxies,
using IFU data from MaNGA and the Tremaine-Weinberg method. Our sample, which
is divided between strongly and weakly barred galaxies identified via Galaxy
Zoo, is the largest that this method has been applied to. We find lower pattern
speeds for strongly barred galaxies than for weakly barred galaxies. As
simulations show that the pattern speed decreases as the bar exchanges angular
momentum with its host, these results suggest that strong bars are more evolved
than weak bars. Interestingly, the corotation radius is not different between
weakly and strongly barred galaxies, despite being proportional to bar length.
We also find that the corotation radius is significantly different between
quenching and star forming galaxies. Additionally, we find that strongly barred
galaxies have significantly lower values for R, the ratio between the
corotation radius and the bar radius, than weakly barred galaxies, despite a
big overlap in both distributions. This ratio classifies bars into ultrafast
bars (R < 1.0; 11% of our sample), fast bars (1.0 < R < 1.4; 27%) and slow bars
(R > 1.4; 62%). Simulations show that R is correlated with the bar formation
mechanism, so our results suggest that strong bars are more likely to be formed
by different mechanisms than weak bars. Finally, we find a lower fraction of
ultrafast bars than most other studies, which decreases the recently claimed
tension with {\Lambda}CDM. However, the median value of R is still lower than
what is predicted by simulations.Comment: 20 pages, 16 figure
From fat droplets to floating forests: cross-domain transfer learning using a PatchGAN-based segmentation model
Many scientific domains gather sufficient labels to train machine algorithms
through human-in-the-loop techniques provided by the Zooniverse.org citizen
science platform. As the range of projects, task types and data rates increase,
acceleration of model training is of paramount concern to focus volunteer
effort where most needed. The application of Transfer Learning (TL) between
Zooniverse projects holds promise as a solution. However, understanding the
effectiveness of TL approaches that pretrain on large-scale generic image sets
vs. images with similar characteristics possibly from similar tasks is an open
challenge. We apply a generative segmentation model on two Zooniverse
project-based data sets: (1) to identify fat droplets in liver cells
(FatChecker; FC) and (2) the identification of kelp beds in satellite images
(Floating Forests; FF) through transfer learning from the first project. We
compare and contrast its performance with a TL model based on the COCO image
set, and subsequently with baseline counterparts. We find that both the FC and
COCO TL models perform better than the baseline cases when using >75% of the
original training sample size. The COCO-based TL model generally performs
better than the FC-based one, likely due to its generalized features. Our
investigations provide important insights into usage of TL approaches on
multi-domain data hosted across different Zooniverse projects, enabling future
projects to accelerate task completion.Comment: 5 pages, 4 figures, accepted for publication at the Proceedings of
the ACM/CIKM 2022 (Human-in-the-loop Data Curation Workshop
Distinguishing Mergers and Disks in High Redshift Observations of Galaxy Kinematics
The majority of massive star-forming galaxies at have velocity
gradients suggestive of rotation, in addition to large amounts of disordered
motions. In this paper, we demonstrate that it is challenging to distinguish
the regular rotation of a disk galaxy from the orbital motions of merging
galaxies with seeing-limited data. However, the merger fractions at
are likely too low for this to have a large effect on measurements of disk
fractions. To determine how often mergers pass for disks, we look to galaxy
formation simulations. We analyze 24000 synthetic images and kinematic
maps of 31 high-resolution simulations of isolated galaxies and mergers at
. We determine if the synthetic observations pass criteria commonly
used to identify disk galaxies, and whether the results are consistent with
their intrinsic dynamical states. Galaxies that are intrinsically mergers pass
the disk criteria for anywhere from 0 to 100 of sightlines. The exact
percentage depends strongly on the specific disk criteria adopted, and weakly
on the separation of the merging galaxies. Therefore, one cannot tell with
certainty whether observations of an individual galaxy indicate a merger or a
disk. To estimate the fraction of mergers passing as disks in current
kinematics samples, we combine the probability that a merger will pass as a
disk with theoretical merger fractions from a cosmological simulation. Taking
the latter at face-value, the observed disk fractions are overestimated by
small amounts: at most by at high stellar mass ( M)
and at low stellar mass ( M).Comment: 15 pages, 10 figures, accepted for publication in Ap
Practical galaxy morphology tools from deep supervised representation learning
Astronomers have typically set out to solve supervised machine learning problems by creating their own representations from scratch. We show that deep learning models trained to answer every Galaxy Zoo DECaLS question learn meaningful semantic representations of galaxies that are useful for new tasks on which the models were never trained. We exploit these representations to outperform several recent approaches at practical tasks crucial for investigating large galaxy samples. The first task is identifying galaxies of similar morphology to a query galaxy. Given a single galaxy assigned a free text tag by humans (e.g. â#diffuseâ), we can find galaxies matching that tag for most tags. The second task is identifying the most interesting anomalies to a particular researcher. Our approach is 100 per cent accurate at identifying the most interesting 100 anomalies (as judged by Galaxy Zoo 2 volunteers). The third task is adapting a model to solve a new task using only a small number of newly-labelled galaxies. Models fine-tuned from our representation are better able to identify ring galaxies than models fine-tuned from terrestrial images (ImageNet) or trained from scratch. We solve each task with very few new labels; either one (for the similarity search) or several hundred (for anomaly detection or fine-tuning). This challenges the longstanding view that deep supervised methods require new large labelled datasets for practical use in astronomy. To help the community benefit from our pretrained models, we release our fine-tuning code zoobot. Zoobot is accessible to researchers with no prior experience in deep learning
Investigating the Effect of Galaxy Interactions on Star Formation at 0.5<z<3.0
Observations and simulations of interacting galaxies and mergers in the local
universe have shown that interactions can significantly enhance the star
formation rates (SFR) and fueling of Active Galactic Nuclei (AGN). However, at
higher redshift, some simulations suggest that the level of star formation
enhancement induced by interactions is lower due to the higher gas fractions
and already increased SFRs in these galaxies. To test this, we measure the SFR
enhancement in a total of 2351 (1327) massive () major
() spectroscopic galaxy pairs at 0.5<z<3.0 with
km s (1000 km s) and projected separation <150 kpc selected from
the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find
that the highest level of SFR enhancement is a factor of 1.23
in the closest projected separation bin (<25 kpc) relative to a stellar mass-,
redshift-, and environment-matched control sample of isolated galaxies. We find
that the level of SFR enhancement is a factor of higher at 0.5<z<1
than at 1<z<3 in the closest projected separation bin. Among a sample of
visually identified mergers, we find an enhancement of a factor of
1.86 for coalesced systems. For this visually identified
sample, we see a clear trend of increased SFR enhancement with decreasing
projected separation (2.40 vs.\ 1.58 for
0.5<z<1.6 and 1.6<z<3.0, respectively). The SFR enhancement seen in our
interactions and mergers are all lower than the level seen in local samples at
the same separation, suggesting that the level of interaction-induced star
formation evolves significantly over this time period.Comment: 23 pages, 13 figures, Accepted for publication in Ap
Optimized Photometric Redshifts for the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS)
We present the first comprehensive release of photometric redshifts
(photo-z's) from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy
Survey (CANDELS) team. We use statistics based upon the Quantile-Quantile
(Q--Q) plot to identify biases and signatures of underestimated or
overestimated errors in photo-z probability density functions (PDFs) produced
by six groups in the collaboration; correcting for these effects makes the
resulting PDFs better match the statistical definition of a PDF. After
correcting each group's PDF, we explore three methods of combining the
different groups' PDFs for a given object into a consensus curve. Two of these
methods are based on identifying the minimum f-divergence curve, i.e., the PDF
that is closest in aggregate to the other PDFs in a set (analogous to the
median of an array of numbers). We demonstrate that these techniques yield
improved results using sets of spectroscopic redshifts independent of those
used to optimize PDF modifications. The best photo-z PDFs and point estimates
are achieved with the minimum f-divergence using the best 4 PDFs for each
object (mFDa4) and the Hierarchical Bayesian (HB4) methods, respectively. The
HB4 photo-z point estimates produced and
outlier fraction = 0.067/0.019 for spectroscopic and
3D-HST redshifts, respectively. Finally, we describe the structure and provide
guidance for the use of the CANDELS photo-z catalogs, which are available at
https://archive.stsci.edu/hlsp/candels.Comment: 35 pages, 19 figures, submitted to ApJ, data available at
https://archive.stsci.edu/hlsp/candel
Major merging history in CANDELS. I. Evolution of the incidence of massive galaxyâgalaxy pairs from z = 3 to z ⌠0
The rate of major galaxyâgalaxy merging is theoretically predicted to steadily increase with redshift during the peak epoch of massive galaxy development (1 †z †3). We use close-pair statistics to objectively study the incidence of massive galaxies (stellar M1 > 2 Ă 1010âMâ) hosting major companions (1 †M1/M2 †4; i.e. 4:1) companions at z > 1. We show that these evolutionary trends are statistically robust to changes in companion proximity. We find disagreements between published results are resolved when selection criteria are closely matched. If we compute merger rates using constant fraction-to-rate conversion factors (Cmerg,pair = 0.6 and Tobs,pair = 0.65âGyr), we find that MR rates disagree with theoretical predictions at z > 1.5. Instead, if we use an evolving Tobs,pair(z) â (1 + z)â2 from Snyder et al., our MR-based rates agree with theory at 0 < z < 3. Our analysis underscores the need for detailed calibration of Cmerg,pair and Tobs,pair as a function of redshift, mass, and companion selection criteria to better constrain the empirical major merger history
The Lyman Continuum Escape Fraction of Star-forming Galaxies at from UVCANDELS
The UltraViolet Imaging of the Cosmic Assembly Near-infrared Deep
Extragalactic Legacy Survey Fields (UVCANDELS) survey is a Hubble Space
Telescope (HST) Cycle-26 Treasury Program, allocated in total 164 orbits of
primary Wide-Field Camera 3 Ultraviolet and Visible light F275W imaging with
coordinated parallel Advanced Camera for Surveys F435W imaging, on four of the
five premier extragalactic survey fields: GOODS-N, GOODS-S, EGS, and COSMOS. We
introduce this survey by presenting a thorough search for galaxies at
that leak significant Lyman continuum (LyC) radiation, as well as
a stringent constraint on the LyC escape fraction () from stacking
the UV images of a population of star-forming galaxies with secure redshifts.
Our extensive search for LyC emission and stacking analysis benefit from the
catalogs of high-quality spectroscopic redshifts compiled from archival
ground-based data and HST slitless spectroscopy, carefully vetted by dedicated
visual inspection efforts. We report a sample of five galaxies as individual
LyC leaker candidates, showing estimated
using detailed Monte Carlo analysis of intergalactic medium attenuation. We
develop a robust stacking method to apply to five samples of in total 85
non-detection galaxies in the redshift range of . Most stacks
give tight 2- upper limits below . A stack
for a subset of 32 emission-line galaxies shows tentative LyC leakage detected
at 2.9-, indicating at ,
supporting the key role of such galaxies in contributing to the cosmic
reionization and maintaining the UV ionization background. These new F275W and
F435W imaging mosaics from UVCANDELS have been made publicly available on the
Barbara A. Mikulski Archive for Space Telescopes.Comment: 33 pages, 21 figures, and 5 tables. Resubmitted after addressing the
referee repor
Constraining the Major Merging History of Massive Galaxies: A Comprehensive Analysis of Close Pairs and Tidal Features Using Empirical and Simulated Data
Title from PDF of title page viewed August 16, 2021Dissertation advisor; Daniel H. McIntoshVitaIncludes bibliographical references (pages 221-239)Thesis (Ph.D.)--Department of Physics and Astronomy and School of Computing and Engineering. University of Missouri--Kansas City, 2021Major galaxy merging is a fundamental aspect of the hierarchical structure-growth scenario of the universe, and it is theoretical expected to contribute to several key aspects of galaxy evolution. As such, empirically identifying major mergers is a key methodological step towards assessing the ``merging -- galaxy evolution'' connection, and close-pair and morphology-based methods are established empirical merger identification techniques. Yet, the merger rate measurements from these methods vary up to a factor of five owing to their unique but analogous systematic biases, especially during the key epoch of galaxy growth (7-11 Gyr ago), highlighting that the merger contribution to galaxy growth remains poorly constrained. As a step towards addressing key open questions pertaining to empirical merger identification methodologies, we carryout comprehensive analysis of close pairs and merging induced tidal features (and in general galactic substructures) using forefront observational data from the Hubble Space Telescope (HST) and realistic mock observations from leading theoretical simulations. We analyze the incidence of major, similar-mass (mass ratio 10.3) from the HST-CANDELS survey and quantify the major merger rate evolution over 11 Gyr in cosmic history (published in Mantha et al., 2018). Using the mock light cone data from the leading SantaCruz Semi-Analytical Model (SAM), we systematically analyze the impact of different observational effects on the measurement of close-pair frequency and provide detailed statistical corrections to account for them. We also developed a new public software tool to extract and quantify different kinds of faint morphological substructures hosted by massive galaxies in the HST imaging and demonstrated its applicability in extracting tidal features using mock observations of a galaxy merger from a cosmological simulation (published in Mantha et al., 2019). Finally, using supervised and unsupervised deep-learning models, we also investigate the automated characterization of different morphological substructures hosted within the parametric light-profile subtracted residual images of 10,000 massive galaxies from the HST CANDELS survey.Major merging history in Candels. I. Evolution of the incidence of massive galaxy-galaxy pairs from Z = 3 to Z ~ 0 -- Studying the physical properties of tidal features I. Extracting morphological substructure in Candels observations and vela simulations -- Major close-pair fraction calibrations using mock realizations from semi-analytical models -- Characterization of residual morphological substructure using supervised and unsupervised deep learning -- Summary and future wor
Harnessing the Hubble Space Telescope Archives:A Catalogue of 21,926 Interacting Galaxies
Mergers play a complex role in galaxy formation and evolution. Continuing to improve our understanding of these systems require ever larger samples, which can be difficult (even impossible) to select from individual surveys. We use the new platform ESA Datalabs to assemble a catalogue of interacting galaxies from the Hubble Space Telescope science archives; this catalogue is larger than previously published catalogues by nearly an order of magnitude. In particular, we apply the Zoobot convolutional neural network directly to the entire public archive of HST images and make probabilistic interaction predictions for 126 million sources from the Hubble Source Catalogue. We employ a combination of automated visual representation and visual analysis to identify a clean sample of 21,926 interacting galaxy systems, mostly with z < 1. 65\% of these systems have no previous references in either the NASA Extragalactic Database or Simbad. In the process of removing contamination, we also discover many other objects of interest, such as gravitational lenses, edge-on protoplanetary disks, and `backlit' overlapping galaxies. We briefly investigate the basic properties of this sample, and we make our catalogue publicly available for use by the community. In addition to providing a new catalogue of scientifically interesting objects imaged by HST, this work also demonstrates the power of the ESA Datalabs tool to facilitate substantial archival analysis without placing a high computational or storage burden on the end user