Engineering topics

Tran, Kim-Vy

Publications and source records attributed to Tran, Kim-Vy.

8 records

DOE OSTI2026

HOLISMOKES XIX

We present imaging and spectroscopic observations of supernova SN 2025wny, associated with the lens candidate PS1 J0716+3821. Photometric monitoring from the Lulin and Maidanak observatories confirms multiple point-like images, consistent with SN 2025wny being strongly lensed by two foreground galaxies. Optical spectroscopy of the brightest image with the Nordic Optical Telescope and the University of Hawaii 88-inch Telescope allowed us to determine the redshift to be z SN = 2.008 ± 0.001, based on narrow absorption lines originating in the interstellar medium of the supernova host galaxy. At this redshift, SN 2025wny shows a very high rest-frame UV flux and broad spectral features even weeks after the explosion, which is consistent with superluminous supernovae of Type I. We find a high ejecta temperature and depressed spectral lines compared to other similar objects. We also measured, for the first time, the redshift of the fainter of the two lens galaxies (the ‘perturber’) to be z p = 0.375 ± 0.001, which is fully consistent with the DESI spectroscopic redshift of the main deflector at z d = 0.3754. Thus, SN 2025wny represents the first confirmed galaxy-scale strongly lensed supernova with time delays likely in the range of days to weeks, as judged from the image separations. This makes SN 2025wny suitable for cosmography, offering a promising new system for independent measurements of the Hubble constant. Following a tradition in the field of strongly lensed supernovae, we give SN 2025wny the nickname SN Winny.

Taubenberger, Stefan↗

DOE OSTI2023

Different higher order kinematics between star-forming and quiescent galaxies based on the SAMI, MAGPI, and LEGA-C surveys

We present the first statistical study of spatially integrated non-Gaussian stellar kinematics spanning 7 Gyr in cosmic time. We use deep, rest-frame optical spectroscopy of massive galaxies (stellar mass $M_\star \gt 10^{10.5} \, \mathrm{M_\odot }$) at redshifts z = 0.05, 0.3, and 0.8 from the SAMI, MAGPI, and LEGA-C surveys, to measure the excess kurtosis h 4 of the stellar velocity distribution, the latter parametrized as a Gauss–Hermite series. We find that at all redshifts where we have large enough samples, h 4 anticorrelates with the ratio between rotation and dispersion, highlighting the physical connection between these two kinematic observables. In addition, and independently from the anticorrelation with rotation-to-dispersion ratio, we also find a correlation between h 4 and M ⋆ , potentially connected to the assembly history of galaxies. In contrast, after controlling for mass, we find no evidence of independent correlation between h 4 and aperture velocity dispersion or galaxy size. These results hold for both star-forming and quiescent galaxies. For quiescent galaxies, h 4 also correlates with projected shape, even after controlling for the rotation-to-dispersion ratio. At any given redshift, star-forming galaxies have lower h 4 compared to quiescent galaxies, highlighting the link between kinematic structure and star-forming activity.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

The Maunakea Spectroscopic Explorer

The Maunakea Spectroscopic Explorer is a next-generation massively multiplexed spectroscopic facility currently under development in Hawaii. It is completely dedicated to large-scale spectroscopic surveys and will enable transformative science. In this white paper we summarize the science case and describe the current state of the project.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2019

The Detailed Science Case for the Maunakea Spectroscopic Explorer, 2019 edition

(Abridged) The Maunakea Spectroscopic Explorer (MSE) is an end-to-end science platform for the design, execution and scientific exploitation of spectroscopic surveys. It will unveil the composition and dynamics of the faint Universe and impact nearly every field of astrophysics across all spatial scales, from individual stars to the largest scale structures in the Universe. Major pillars in the science program for MSE include (i) the ultimate Gaia follow-up facility for understanding the chemistry and dynamics of the distant Milky Way, including the outer disk and faint stellar halo at high spectral resolution (ii) galaxy formation and evolution at cosmic noon, via the type of revolutionary surveys that have occurred in the nearby Universe, but now conducted at the peak of the star formation history of the Universe (iii) derivation of the mass of the neutrino and insights into inflationary physics through a cosmological redshift survey that probes a large volume of the Universe with a high galaxy density. MSE is positioned to become a critical hub in the emerging international network of front-line astronomical facilities, with scientific capabilities that naturally complement and extend the scientific power of Gaia, the Large Synoptic Survey Telescope, the Square Kilometer Array, Euclid, WFIRST, the 30m telescopes and many more.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2017

Deep CO(1–0) Observations of z = 1.62 Cluster Galaxies with Substantial Molecular Gas Reservoirs and Normal Star Formation Efficiencies

We present an extremely deep CO(1–0) observation of a confirmed z = 1.62 galaxy cluster. We detect two spectroscopically confirmed cluster members in CO(1–0) with signal-to-noise ratio >5. Both galaxies have log(M{sub ⋆}/M{sub ⊙}) > 11 and are gas rich, with M{sub mol}/(M{sub ⋆}+M{sub mol}) ∼ 0.17–0.45. One of these galaxies lies on the star formation rate (SFR)–M{sub ⋆} sequence, while the other lies an order of magnitude below. We compare the cluster galaxies to other SFR-selected galaxies with CO measurements and find that they have CO luminosities consistent with expectations given their infrared luminosities. We also find that they have gas fractions and star formation efficiencies (SFE) comparable to what is expected from published field galaxy scaling relations. The galaxies are compact in their stellar light distribution, at the extreme end for all high-redshift star-forming galaxies. However, their SFE is consistent with other field galaxies at comparable compactness. This is similar to two other sources selected in a blind CO survey of the HDF-N. Despite living in a highly quenched protocluster core, the molecular gas properties of these two galaxies, one of which may be in the process of quenching, appear entirely consistent with field scaling relations between the molecular gas content, stellar mass, star formation rate, and redshift. We speculate that these cluster galaxies cannot have any further substantive gas accretion if they are to become members of the dominant passive population in z<1 clusters.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

A STUDY OF CENTRAL GALAXY ROTATION WITH STELLAR MASS AND ENVIRONMENT

We present a pilot analysis of the influence of galaxy stellar mass and cluster environment on the probability of slow rotation in 22 central galaxies at mean redshift z = 0.07. This includes new integral-field observations of five central galaxies selected from the Sloan Digital Sky Survey, observed with the SPIRAL integral-field spectrograph on the Anglo-Australian Telescope. The composite sample presented here spans a wide range of stellar masses, 10.9 < log(M{sub ∗}/M{sub ⊙})<12.0, and are embedded in halos ranging from groups to clusters, 12.9 < log(M{sub 200}/M{sub ⊙})<15.6. We find a mean probability of slow rotation in our sample of P(SR) = 54±7%. Our results show an increasing probability of slow rotation in central galaxies with increasing stellar mass. However, when we examine the dependence of slow rotation on host cluster halo mass, we do not see a significant relationship. We also explore the influence of cluster dominance on slow rotation in central galaxies. Clusters with low dominance are associated with dynamically younger systems. We find that cluster dominance has no significant effect on the probability of slow rotation in central galaxies. These results conflict with a paradigm in which halo mass alone predetermines central galaxy properties.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

ZFIRE: a Keck/MOSFIRE spectroscopic survey of galaxies in rich environments at z ∼ 2

We present an overview and the first data release of ZFIRE, a spectroscopic redshift survey of star-forming galaxies that utilizes the MOSFIRE instrument on Keck-I to study galaxy properties in rich environments at 1.5 < z < 2.5. ZFIRE measures accurate spectroscopic redshifts and basic galaxy properties derived from multiple emission lines. The galaxies are selected from a stellar mass limited sample based on deep near infrared imaging (K{sub AB}<25) and precise photometric redshifts from the ZFOURGE and UKIDSS surveys as well as grism redshifts from 3DHST. Between 2013 and 2015, ZFIRE has observed the COSMOS and UDS legacy fields over 13 nights and has obtained 211 galaxy redshifts over 1.57 < z < 2.66 from a combination of nebular emission lines (such as Hα, [N ii], Hβ, [O ii], [O iii], and [S ii]) observed at 1–2 μm. Based on our medium-band near infrared photometry, we are able to spectrophotometrically flux calibrate our spectra to ∼10% accuracy. ZFIRE reaches 5σ emission line flux limits of ∼3 × 10{sup −18} erg s{sup −1} cm{sup −2} with a resolving power of R = 3500 and reaches masses down to ∼10{sup 9} M {sub ⊙}. We confirm that the primary input survey, ZFOURGE, has produced photometric redshifts for star-forming galaxies (including highly attenuated ones) accurate to Δz/(1+z{sub spec})=0.015 with 0.7% outliers. We measure a slight redshift bias of <0.001, and we note that the redshift bias tends to be larger at higher masses. We also examine the role of redshift on the derivation of rest-frame colors and stellar population parameters from SED fitting techniques. The ZFIRE survey extends spectroscopically confirmed z ∼ 2 samples across a richer range of environments, here we make available the first public release of the data for use by the community.{sup 7}.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Spatial correlation between dust and hα emission in dwarf irregular galaxies

Using a sample of dwarf irregular galaxies selected from the ALFALFA blind H i-survey and observed using the VIMOS IFU, we investigate the relationship between Hα emission and Balmer optical depth (τ{sub b}). We find a positive correlation between Hα luminosity surface density and Balmer optical depth in 8 of 11 at ≥0.8σ significance (6 of 11 at ≥1.0σ) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearman’s rank correlation coefficient to test for correlation between Σ{sub Hα} and τ{sub b} in all the galaxies combined, we find ρ=0.39, indicating a positive correlation at 4σ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between Hα luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.

79 ASTRONOMY AND ASTROPHYSICS↗