41 research outputs found
A Multidimensional View on the Emission-line Diagnostics of the Warm Ionized Gas in Nearby Galaxies
The baryonic cycle, being a fundamental process that shapes the cosmic ecosystem, describes the transformation and migration of baryonic matter in different phases. The warm ionized interstellar medium (ISM), defined as low-density gas that has temperature of the order of 10,000 K, represents an important link of the baryonic cycle and can be produced by a variety of energetic activities in galaxies, such as star formations, active galactic nuclei, and so forth. More importantly, the formation and evolution of the warm ionized gas not only traces the ongoing activities of the galaxies, but also reveals the past evolution of galaxies through its chemical imprint.
Observationally, since the warm ionized gas produces a series of detectable emission lines in the optical that traces the abundances and ionization states of different elements, it has been the main subject of the chemical evolution studies of galaxies. By decoding the emission-line spectra from the ionized gas, we can learn about how different elements are released into the ISM from generations of stars and how they in turn regulate the star-formation activities. Meanwhile, the ionization states of the elements reflect the ionizing energies and feedback mechanisms in galaxies.
However, converting the observed spectra to the properties of the ionized gas is a notoriously difficult task and has a lot of uncertainties. To obtain a better understanding of the physical properties of the warm ionized gas, I studied the emission-line spectra from a large sample of galaxies in Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (SDSS-IV MaNGA) and computed a large grid of photoionization models to describe the observations. With these data and models, I established a novel multidimensional analysis method of emission-line ratios from the ionized gas. Using this method, I made new discoveries on the ionization mechanisms, spatial distribution, and dynamical evolution of the warm ionized gas. Moreover, I show that the current modeling approach for the warm ionized gas needs to be improved and more realistic treatment of the small-scale structures are vital for correctly interpreting the emission-line spectra. The multidimensional view on the emission-line diagnostics has great potential for future studies on the high-redshift galaxies as well as local interstellar medium
Upper boundaries of active galactic nucleus regions in optical diagnostic diagrams
The distribution of galaxies in optical diagnostic diagrams can provide information about their physical parameters when compared with ionization models under proper assumptions. By using a sample of central emitting regions from the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA), we find evidence of the existence of upper boundaries for narrow-line regions (NLRs) of active galactic nuclei (AGNs) in optical Baldwin, Phillips & Terlevich (BPT) diagrams, especially in diagrams involving [S ii]λλ6716, 6731/Hα. Photoionization models can reproduce the boundaries well, as a consequence of the decrease of [S ii]λλ6716, 6731/Hα and [O iii]λ5007/Hβ ratios at very high metallicity. Whilst the exact location of the upper boundary in the [S ii] BPT diagram depends only weakly on the electron density of the ionized cloud and the secondary nitrogen prescription, its dependence on the shapes of the input spectral energy distributions (SEDs) is much stronger. This allows us to constrain the power-law index of the AGN SED between 1 Ryd and ∼100 Ryd to be less than or equal to −1.40 ± 0.05. The coverage of photoionization models in the [N ii] BPT diagram has a stronger dependence on the electron density and the secondary nitrogen prescription. With the density constrained by the [S ii] doublet ratio and the input SED constrained by the [S ii] BPT diagram, we find that the extent of the data in the [N ii] BPT diagram favours those prescriptions with high N/O ratios. Although shock-ionized clouds can produce line ratios similar to those from photoionization, the resulting shapes of the upper boundaries, if they exist, would likely be different from those of photoionizing origin
Upper boundaries of AGN regions in optical diagnostic diagrams
The distribution of galaxies in optical diagnostic diagrams can provide
information about their physical parameters when compared with ionization
models under proper assumptions. By using a sample of central emitting regions
from the MaNGA survey, we find evidence of the existence of upper boundaries
for narrow-line regions (NLRs) of active galactic nuclei (AGN) in optical BPT
diagrams, especially in the diagrams involving [S II]6716,
6731/H. Photoionization models can well reproduce the boundaries as a
consequence of the decrease of [S II]6716, 6731/H and
[O III]5007/H ratios at very high metallicity. Whilst the exact
location of the upper boundary in the [S II] BPT diagram only weakly depends on
the electron density of the ionized cloud and the secondary nitrogen
prescription, its dependence on the shapes of the input SEDs is much stronger.
This allows us to constrain the power-law index of the AGN SED between 1 Ryd
and Ryd to be less than or equal to . The coverage of
the photoionization models in the [N II] BPT diagram has a stronger dependence
on the electron density and the secondary nitrogen prescription. With the
density constrained by the [S II] doublet ratio and the input SED constrained
by the [S II] BPT diagram, we find that the extent of the data in the [N II]
BPT diagram favors those prescriptions with high N/O ratios. Although
shock-ionized cloud can produce similar line ratios as those by
photoionization, the resulting shapes of the upper boundaries, if exist, would
likely be different from those of a photoionizing origin.Comment: 17 pages, 19 figures, accepted by MNRA
Self-Consistent Grain Depletions and Abundances II: Effects on strong-line diagnostics of extragalactic H II regions
The depletion of elements onto dust grains is characterized using a
generalized depletion strength for any sightline, and trend-line
parameters and . The parameters and define the
relative depletion pattern, for which values are published in previous works.
The present study uses these parameters to calculate post-depleted gas-phase
abundances of 15 different elements while varying from 0 to 1. An
analysis of emergent strong spectral line intensities, obtained by inputting
the calculated abundances into a cloudy model, shows that the depletion
strength has a non-trivial effect on predicted emission lines and the thermal
balance of the ionized cloud. The amount by which elements deplete also affects
the coolant abundances in the gas. Furthermore, it was found that each of the
parameters - metallicity, ionization parameter U and depletion strength
have degenerate effects on the emission-line strengths, and thermal balance of
the interstellar medium (ISM). Finally, comparing our results to a sample of H
II regions using data obtained from the Mapping Nearby Galaxies at Apache Point
Observatory survey (MaNGA) revealed that the best-fit was approximately
0.5. However, this best-fit value does not work well for all metallicities.
Removing the sulfur depletion and changing the nitrogen abundance pattern can
improve the fit. As a result, extra observational evidence is required to
verify the choices of parameters and better constrain the typical depletion
strength in galaxies.Comment: 11 pages, 5 figure
The Data Analysis Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey: Emission-Line Modeling
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the
largest integral-field spectroscopy survey to date, aiming to observe a
statistically representative sample of 10,000 low-redshift galaxies. In this
paper we study the reliability of the emission-line fluxes and kinematic
properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the
algorithmic choices made in the DAP with regards to measuring emission-line
properties, and the effect of our adopted strategy of simultaneously fitting
the continuum and line emission. The effect of random errors are quantified by
studying various fit-quality metrics, idealized recovery simulations and repeat
observations. This analysis demonstrates that the emission lines are well-fit
in the vast majority of the MaNGA dataset and the derived fluxes and errors are
statistically robust. The systematic uncertainty on emission-line properties
introduced by the choice of continuum templates is also discussed. In
particular, we test the effect of using different stellar libraries and simple
stellar-population models on the derived emission-line fluxes and the effect of
introducing different tying prescriptions for the emission-line kinematics. We
show that these effects can generate large ( 0.2 dex) discrepancies at low
signal-to-noise and for lines with low equivalent width (EW); however, the
combined effect is noticeable even for H EW 6~\AA. We provide
suggestions for optimal use of the data provided by SDSS data release 15 and
propose refinements on the \DAP\ for future MaNGA data releases.Comment: accepted on A
The need for multicomponent dust attenuation in modeling nebular emission: Constraints from SDSS-IV MaNGA
A fundamental assumption adopted in nearly every extragalactic emission-line
study is that the attenuation of different emission lines can be described by a
single attenuation curve. Here we show this assumption fails in many cases with
important implications for derived results. We developed a new method to
measure the differential nebular attenuation among three kinds of transitions:
the Balmer lines of hydrogen, high-ionization transitions, and low-ionization
transitions. This method bins the observed data in a multidimensional space
spanned by attenuation-insensitive line ratios. Within each small bin, the
variations in line ratios are mainly driven by the variations in the nebular
attenuation. This allows us to measure the nebular attenuation using both
forbidden lines and Balmer lines. We applied this method to a sample of 2.4
million star-forming spaxels from SDSS-IV MaNGA. We found that the attenuation
of high ionization lines and Balmer lines can be well described by a single
Fitzpatrick (1999) extinction curve with . However, no single
attenuation curve can simultaneously account for all three transitions. This
strongly suggests that different lines have different effective attenuations,
likely because spectroscopy at kiloparsec resolutions mixes multiple regions
with different intrinsic line ratios and different levels of attenuation. As a
result, the assumption that different lines follow the same attenuation curve
breaks down. Using a single attenuation curve determined by Balmer lines to
correct attenuation-sensitive forbidden line ratios could bias the nebular
parameters derived by 0.06--0.25 dex at , depending on the details of
the dust attenuation model. Observations of a statistically large sample of H
II regions with high spatial resolutions and large spectral coverage are vital
for improved modeling and deriving accurate corrections for this effect.Comment: 28 pages, 17 figures, published in A&
Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging
The outstanding performance of organic-inorganic metal trihalide solar cells benefits from the
exceptional photo-physical properties of both electrons and holes in the material. Here, we
directly probe the free-carrier dynamics in Cs-doped FAPbI3 thin films by spatiotemporal
photoconductivity imaging. Using charge transport layers to selectively quench one type of
carriers, we show that the two relaxation times on the order of 1 μs and 10 μs correspond to
the lifetimes of electrons and holes in FACsPbI3, respectively. Strikingly, the diffusion map-
ping indicates that the difference in electron/hole lifetimes is largely compensated by their
disparate mobility. Consequently, the long diffusion lengths (3~5 μm) of both carriers are
comparable to each other, a feature closely related to the unique charge trapping and de-
trapping processes in hybrid trihalide perovskites. Our results unveil the origin of superior
diffusion dynamics in this material, crucially important for solar-cell applications.The research at UT-Austin was primarily supported by the NSF through the Center for Dynamics and Control of Materials, an NSF Materials Research Science and Engineering Center (MRSEC) under Cooperative Agreement DMR-1720595. The authors also acknowledge the use of facilities and instrumentation supported by the NSF MRSEC. K.L. and X.M. acknowledge the support from Welch Foundation Grant F-1814. X. Li acknowledges the support from Welch Foundation Grant F-1662. The tip-scan iMIM setup was supported by the US Army Research Laboratory and the US Army Research Office under Grants W911NF-16-1-0276 and W911NF-17-1-0190. The work at NREL was supported by the US DOE under Contract No. DE-AC36-08GO28308 with Alliance for Sustainable Energy, Limited Liability Company (LLC), the Manager and Operator of the National Renewable Energy Laboratory. K.Z., J.H., X.C., X.W., and Y.Y. acknowledge the support on charge carrier dynamics study from the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the US DOE. F.Z. acknowledges the support on devices fabrication and characterizations from the De-Risking Halide PSCs program of the National Center for Photovoltaics, funded by the US DOE, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office.Center for Dynamics and Control of Material
The data analysis pipeline for the SDSS-IV MaNGA IFU Galaxy Survey : overview
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is acquiring integral-field spectroscopy for the largest sample of galaxies to date. By 2020, the MaNGA Survey - one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) - will have observed a statistically representative sample of 104 galaxies in the local Universe z ∼99%) of analyzed spectra. We summarize assessments of the precision and accuracy of our measurements as a function of signal-to-noise, and provide specific guidance to users regarding the limitations of the data. The MaNGA DAP software is publicly available and we encourage community involvement in its development.PostprintPeer reviewe
The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar and APOGEE-2 Data
This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys