arXiv subjects

Kyle Westfall

Publications and source records attributed to Kyle Westfall.

17 recordsLinked to original sources

arXiv2026

MSA-3D: Rotation Curves and Dark Matter Fractions at z~0.5-1.7 with JWST/NIRSpec

We present rotation curves and inner mass distributions for 30 star-forming galaxies at $0.5<z<1.7$, observed with JWST/NIRSpec as part of the MSA-3D Cycle 1 survey. Combining spatially resolved ionised-gas kinematics with JWST/NIRCam imaging, we constrain baryonic and dark matter contributions through forward dynamical modelling for galaxies extending down to stellar masses of $\sim10^{9}M_\odot$. For the 23 galaxies in our primary statistical sample, we find predominantly rotationally supported disks with intrinsic dispersions $\sigma_0\sim31$-65 km s$^{-1}$ and a wide range of dark matter fractions, $f_{DM}(R_e)\sim0.1$-0.9, with a median of 0.63 and substantial galaxy-to-galaxy scatter of $\sim0.2$ dex. These results are supported by a complementary consistency check using stellar mass maps and SFR-derived gas profiles. Among the 19 galaxies reaching $\gtrsim2R_e$, we identify six rising, six flat, and seven falling rotation curves. These classes define an observed ordering from rotationally dominated, dark-matter-rich disks ($V_{rot}/\sigma_0\approx4$, $f_{DM}\gtrsim0.7$) to more dispersion-supported systems with centrally concentrated baryonic mass distributions ($V_{rot}/\sigma_0\approx2$, $f_{DM}\lesssim0.55$). The stellar Tully-Fisher relation lies close to the local relation evolved under the adopted self-similar $\Lambda$CDM scaling. A simplified seeing-degradation test shifts the inferred normalisation by ~0.2 dex at fixed $V_c$, suggesting that spatial resolution contributes to, but does not fully explain, differences among high-redshift Tully-Fisher measurements. Overall, MSA-3D provides a high-resolution extension of previous surveys toward lower stellar masses, spanning $9.0 < \log(M_\star/M_\odot) < 11.2$, and reinforces that star-forming disks near $z\sim1$ span a broad range of dynamical states and inner mass distributions.

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arXiv2024

Ionized gas in quiescent galaxies: Temperature measurement and constraint on the ionization source

In non-star-forming, passively evolving galaxies, regions with emission lines dominated by low-ionization species are classified as Low-Ionization Emission Regions (LIERs). The ionization mechanism behind such regions has long been a mystery. Active Galactic Nuclei (AGNs), which were once believed to be the source, have been found not to be the dominant mechanism, especially in regions distant from the galaxy nuclei. The remaining candidates, photoionization by post-Asymtopic Giant Branch (pAGB) stars and interstellar shocks can only be distinguished with in-depth analysis. As the temperature predictions of these two models differ, temperature measurements can provide strong constraints on this puzzle. We selected a sample of 2795 quiescent red-sequence galaxies from the Sloan Digital Sky Survey IV (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We divided the sample spectra into three groups based on their [N II]/H$\alpha$ flux ratio and utilized stacking techniques to improve the signal-to-noise ratio of the observed spectra. We determined the temperature of [O III], [N II], [S II], and [O II] through their temperature-sensitive emission line ratios. Subsequently, we compared the measured temperatures with predictions from different models. The results demonstrate consistency with the interstellar shock model with preshock density n = 1 cm$^{-3}$ and solar metallicity, thus supporting shocks as the dominant ionization source of LIERs. Additionally, we also find that the interstellar dust extinction value measured through the Balmer decrement appears to be larger than that implied by the forbidden line ratios of low-ionization lines.

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arXiv2024

SDSS-IV MaNGA: Calibration of astrophysical line-widths in the H{\alpha} region using HexPak observations

We have re-observed $\rm\sim$40 low-inclination, star-forming galaxies from the MaNGA survey ($\upsigma\sim65$~\kms) at $\sim$6.5 times higher spectral resolution ($\upsigma\sim10$~\kms) using the HexPak integral field unit on the WIYN 3.5m telescope. The aim of these observations is to calibrate MaNGA's instrumental resolution and to characterize turbulence in the warm interstellar medium and ionized galactic outflows. Here we report the results for the H$\rm\upalpha$ region observations as they pertain to the calibration of MaNGA's spectral resolution. Remarkably, we find that the previously-reported MaNGA line-spread-function (LSF) Gaussian width is systematically underestimated by only 1\%. The LSF increase modestly reduces the characteristic dispersion of HII regions-dominated spectra sampled at 1-2 kpc spatial scales from 23 to 20 km s$^{-1}$ in our sample, or a 25\% decrease in the random-motion kinetic energy. This commensurately lowers the dispersion zeropoint in the relation between line-width and star-formation rate surface-density in galaxies sampled on the same spatial scale. This modest zero-point shift does not appear to alter the power-law slope in the relation between line-width and star-formation rate surface-density. We also show that adopting a scheme whereby corrected line-widths are computed as the square root of the median of the difference in the squared measured line width and the squared LSF Gaussian avoids biases and allows for lower SNR data to be used reliably.

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arXiv2023

The Future of Astronomical Data Infrastructure: Meeting Report

The astronomical community is grappling with the increasing volume and complexity of data produced by modern telescopes, due to difficulties in reducing, accessing, analyzing, and combining archives of data. To address this challenge, we propose the establishment of a coordinating body, an "entity," with the specific mission of enhancing the interoperability, archiving, distribution, and production of both astronomical data and software. This report is the culmination of a workshop held in February 2023 on the Future of Astronomical Data Infrastructure. Attended by 70 scientists and software professionals from ground-based and space-based missions and archives spanning the entire spectrum of astronomical research, the group deliberated on the prevailing state of software and data infrastructure in astronomy, identified pressing issues, and explored potential solutions. In this report, we describe the ecosystem of astronomical data, its existing flaws, and the many gaps, duplication, inconsistencies, barriers to access, drags on productivity, missed opportunities, and risks to the long-term integrity of essential data sets. We also highlight the successes and failures in a set of deep dives into several different illustrative components of the ecosystem, included as an appendix.

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arXiv2021

Signatures of inflowing gas in red geyser galaxies hosting radio-AGN

We study cool neutral gas traced by NaD absorption in 140 local ($\rm z<0.1)$ early-type ``red geyser'' galaxies. These galaxies show unique signatures in spatially-resolved strong-line emission maps that have been interpreted as large-scale active galactic nuclei driven ionized winds. To investigate the possible fuel source for these winds, we examine the abundance and kinematics of cool gas ($\rm T \sim 100-1000 K$) inferred from Na I D absorption in red geysers and matched control samples drawn from SDSS-IV MaNGA. We find that red geysers host greater amounts of NaD-associated material. Substantial cool gas components are detected in more than $\rm 50 \%$ of red geysers (compared to 25\% of the control sample) going up to 78$\%$ for radio-detected red geysers. Our key result is that cool gas in red geysers is predominantly infalling. Among our 30 radio-detected red geysers, 86$\%$ show receding NaD absorption velocities (with respect to the systemic velocity) between $\rm 40 - 50~km~s^{-1}$. We verify this result by stacking NaD profiles across each sample which confirms the presence of infalling NaD velocities within red geysers ( $\sim\rm 40~km~s^{-1}$) with no velocity offsets detected in the control samples. Interpreting our observations as signatures of inflowing cool neutral clouds, we derive an approximate mass inflow rate of $\rm \dot{M}_{in} \sim 0.1 M_{\odot} yr^{-1}$, similar to that expected from minor merging and internal recycling. Some red geysers show much higher rates ($\rm \dot{M}_{in} \sim 5 M_{\odot} yr^{-1}$) that may indicate an ongoing accretion event.

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arXiv2021

Evidence of wind signatures in the gas velocity profiles of Red Geysers

Spatially resolved spectroscopy from SDSS-IV MaNGA survey has revealed a class of quiescent, relatively common early-type galaxies, termed "red geysers", that possibly host large scale active galactic nuclei driven winds. Given their potential importance in maintaining low level of star formation at late times, additional evidence confirming that winds are responsible for the red geyser phenomenon is critical. In this work, we present follow-up observations with the Echellette Spectrograph and Imager (ESI) at the Keck telescope of two red geysers (z$<$0.1) using multiple long slit positions to sample different regions of each galaxy. Our ESI data with a spectral resolution (R) $\sim$ 8000 improves upon MaNGA's resolution by a factor of four, allowing us to resolve the ionized gas velocity profiles along the putative wind cone with an instrumental resolution of $\rm \sigma = 16~km~s^{-1}$. The line profiles of H$\alpha$ and [NII]$\rm \lambda 6584$ show asymmetric shapes that depend systematically on location $-$ extended blue wings on the red-shifted side of the galaxy and red wings on the opposite side. We construct a simple wind model and show that our results are consistent with geometric projections through an outflowing conical wind oriented at an angle towards the line of sight. An alternative hypothesis that assigns the asymmetric pattern to "beam-smearing" of a rotating, ionized gas disk does a poor job matching the line asymmetry profiles. While our study features just two sources, it lends further support to the notion that red geysers are the result of galaxy-scale winds.

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arXiv2018

Marvin: A Toolkit for Streamlined Access and Visualization of the SDSS-IV MaNGA Data Set

The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, one of three core programs of the fourth-generation Sloan Digital Sky Survey (SDSS-IV), is producing a massive, high-dimensional integral field spectroscopic data set. However, leveraging the MaNGA data set to address key questions about galaxy formation presents serious data-related challenges due to the combination of its spatially inter-connected measurements and sheer volume. For each galaxy, the MaNGA pipelines produce relatively large data files to preserve the spatial correlations of the spectra and measurements, but this comes at the expense of storing the data set in a coarsely-chunked manner. The coarse chunking and total volume of the data make it time-consuming to download and curate locally-stored data. Thus, accessing, querying, visually exploring, and performing statistical analyses across the whole data set at a fine-grained scale is extremely challenging using just FITS files. To overcome these challenges, we have developed \marvin: a toolkit consisting of a Python package, Application Programming Interface (API), and web application utilizing a remote database. \marvin's robust and sustainable design minimizes maintenance, while facilitating user-contributed extensions such as high level analysis code. Finally, we are in the process of abstracting out \marvin's core functionality into a separate product so that it can serve as a foundation for others to develop \marvin-like systems for new science applications.

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arXiv2018

Detecting Radio-AGN signatures in Red geysers

A new class of quiescent galaxies harboring possible AGN-driven winds has been discovered using spatially resolved optical spectroscopy from the ongoing SDSS-IV MaNGA survey. These galaxies, termed "red geysers", constitute $5-10\%$ of the local quiescent population and are characterized by narrow bisymmetric patterns in ionized gas emission features. Cheung et al. argued that these galaxies host large-scale AGN-driven winds that may play a role in suppressing star formation at late times. In this work, we test the hypothesis that AGN activity is ultimately responsible for the red geyser phenomenon. We compare the nuclear radio activity of the red geysers to a matched control sample with similar stellar mass, redshift, rest frame $NUV-r$ color, axis ratio and presence of ionized gas. We have used the 1.4 GHz radio continuum data from VLA FIRST survey to stack the radio flux from the red geyser and control samples. In addition to a 3 times higher FIRST detection rate, we find that red geysers have a 5$\sigma$ higher level of average radio flux than control galaxies. After restricting to rest-frame $NUV-r$ color $>$ 5 and checking mid-IR WISE photometry, we rule out star formation contamination and conclude that red geysers are associated with more active AGN. Red geysers and a possibly-related class with disturbed H$\alpha$ emission account for 40\% of all radio-detected red galaxies with $\rm log~(M_\star/M_\odot) < 11$. Our results support a picture in which episodic AGN activity drives large-scale-relatively weak ionized winds that may provide a feedback mechanism for many early-type galaxies.

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arXiv2018

A direct test of density wave theory in a grand-design spiral galaxy

The exact nature of the arms of spiral galaxies is still an open question. It has been widely assumed that spiral arms in galaxies with two distinct symmetrical arms are the products of density waves that propagate around the disk, with the spiral arms being visibly enhanced by the star formation that is triggered as the passing wave compresses gas in the galaxy disk. Such a persistent wave would propagate with an approximately constant angular speed, its pattern speed Op. The quasi-stationary density wave theory can be tested by measuring this quantity and showing that it does not vary with radius in the galaxy. Unfortunately, this measurement is difficult because Op is only indirectly connected to observables such as the stellar rotation speed. Here, we use the detailed information on stellar populations of the grand-design spiral galaxy UGC 3825, extracted from spectral mapping, to measure the offset between young stars of a known age and the spiral arm in which they formed, allowing the first direct measure of Op at a range of radii. The offset in this galaxy is found to be as expected for a pattern speed that varies little with radius, indicating consistency with a quasi-stationary density wave, and lending credence to this new method.

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arXiv2018

SDSS IV MaNGA: Characterizing Non-Axisymmetric Motions in Galaxy Velocity Fields Using the Radon Transform

We show how the Radon transform (defined as a series of line integrals through an image at different orientations and offsets from the origin) can be used as a simple, non-parametric tool to characterize galaxy velocity fields, specifically their global kinematic position angles (PA_k) and any radial variation or asymmetry in PA_k. This method is fast and easily automated, making it particularly beneficial in an era where IFU and interferometric surveys are yielding samples of thousands of galaxies. We demonstrate the Radon transform by applying it to gas and stellar velocity fields from the first ~2800 galaxies of the SDSS-IV MaNGA IFU survey. We separately classify gas and stellar velocity fields into five categories based on the shape of their radial PA_k profiles. At least half of stellar velocity fields and two-thirds of gas velocity fields are found to show detectable deviations from uniform coplanar circular motion, although most of these variations are symmetric about the center of the galaxy. The behavior of gas and stellar velocity fields is largely independent, even when PA_k profiles for both components are measured over the same radii. We present evidence that one class of symmetric PA_k variations is likely associated with bars and/or oval distortions, while another class is more consistent with warped disks. This analysis sets the stage for more in-depth future studies which explore the origin of diverse kinematic behavior in the galaxy population.

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arXiv2017

SDSS-IV MaNGA: Constraints on the Conditions for Star Formation in Galaxy Discs

Regions of disc galaxies with widespread star formation tend to be both gravitationally unstable and self-shielded against ionizing radiation, whereas extended outer discs with little or no star formation tend to be stable and unshielded on average. We explore what drives the transition between these two regimes, specifically whether discs first meet the conditions for self-shielding (parameterized by dust optical depth, $\tau$) or gravitational instability (parameterized by a modified version of Toomre's instability parameters, $Q_{\rm thermal}$, which quantifies the stability of a gas disc that is thermally supported at $T=10^4$ K). We first introduce a new metric formed by the product of these quantities, $Q_{\rm thermal}\tau$, which indicates whether the conditions for disk instability or self-shielding are easier to meet in a given region of a galaxy, and we discuss how $Q_{\rm thermal}\tau$ can be constrained even in the absence of direct gas information. We then analyse a sample of 13 galaxies with resolved gas measurements and find that on average galaxies will reach the threshold for disk instabilities ($Q_{\rm thermal}<1$) before reaching the threshold for self-shielding ($\tau>1$). Using integral field spectroscopic observations of a sample of 236 galaxies from the MaNGA survey, we find that the value of $Q_{\rm thermal}\tau$ in star-forming discs is consistent with similar behavior. These results support a scenario where disc fragmentation and collapse occurs before self-shielding, suggesting that gravitational instabilities are the primary condition for widespread star formation in galaxy discs. Our results support similar conclusions based on recent galaxy simulations.

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arXiv2017

SDSS-IV MaNGA: The Spatial Distribution of Star Formation and its Dependence on Mass, Structure and Environment

We study the spatially resolved star formation of 1494 galaxies in the SDSSIV-MaNGA Survey. SFRs are calculated using a two-step process, using $H_\alpha$ in star forming regions and $D_n4000$ in regions identified as AGN/LI(N)ER or lineless. The roles of secular and environmental quenching processes are investigated by studying the dependence of the radial profiles of specific star formation rate on stellar mass, galaxy structure and environment. We report on the existence of `Centrally Suppressed' galaxies, which have suppressed SSFR in their cores compared to their disks. The profiles of centrally suppressed and unsuppressed galaxies are distibuted in a bimodal way. Galaxies with high stellar mass and core velocity dispersion are found to be much more likely to be centrally suppressed than low mass galaxies, and we show that this is related to morphology and the presence of AGN/LI(N)ER like emission. Centrally suppressed galaxies also display lower star formation at all radii compared to unsuppressed galaxies. The profiles of central and satellite galaxies are also compared, and we find that satellite galaxies experience lower specific star formation rates at all radii than central galaxies. This uniform suppression could be a signal of the stripping of hot halo gas in the process known as strangulation. We find that satellites are not more likely to be suppressed in their cores than centrals, indicating that the core suppression is an entirely internal process. We find no correlation between the local environment density and the profiles of star formation rate surface density.

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arXiv2017

SDSS IV MaNGA - Metallicity and nitrogen abundance gradients in local galaxies

We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star forming regions in a representative sample of 550 nearby galaxies in the stellar mass range $\rm 10^9-10^{11.5} M_\odot$ with resolved spectroscopic data from the SDSS-IV MaNGA survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius ($\rm R_e$), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with $\rm log(M_\star/M_\odot) = 9.0$ but exhibiting slopes as steep as -0.14 dex $\rm R_e^{-1}$ at $\rm log(M_\star/M_\odot) = 10.5$ (using R23, but equivalent results are obtained using O3N2). At higher masses, these slopes remain typical in the outer regions of our sample ($\rm R > 1.5 ~R_e$), but a flattening is observed in the central regions ($\rm R < 1~ R_e$). In the outer regions ($\rm R > 2.0 ~R_e$) we detect a mild flattening of the metallicity gradient in stacked profiles, although with low significance. The N/O ratio gradient provides complementary constraints on the average chemical enrichment history. Unlike the oxygen abundance, the average N/O profiles do not flatten out in the central regions of massive galaxies. The metallicity and N/O profiles both depart significantly from an exponential form, suggesting a disconnect between chemical enrichment and stellar mass surface density on local scales. In the context of inside-out growth of discs, our findings suggest that central regions of massive galaxies today have evolved to an equilibrium metallicity, while the nitrogen abundance continues to increase as a consequence of delayed secondary nucleosynthetic production.

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arXiv2016

SDSS-IV MaNGA: stellar population gradients as a function of galaxy environment

We study the internal radial gradients of stellar population properties within $1.5\;R_{\rm e}$ and analyse the impact of galaxy environment. We use a representative sample of 721 galaxies with masses ranging between $10^{9}\;M_{\odot}$ to $10^{11.5}\;M_{\odot}$ from the SDSS-IV survey MaNGA. We split this sample by morphology into early-type and late-type galaxies. Using the full spectral fitting code FIREFLY, we derive the light and mass-weighted stellar population properties age and metallicity, and calculate the gradients of these properties. We use three independent methods to quantify galaxy environment, namely the $N^{th}$ nearest neighbour, the tidal strength parameter $Q$ and distinguish between central and satellite galaxies. In our analysis, we find that early-type galaxies generally exhibit shallow light-weighted age gradients in agreement with the literature and mass-weighted median age gradients tend to be slightly positive. Late-type galaxies, instead, have negative light-weighted age gradients. We detect negative metallicity gradients in both early and late-type galaxies that correlate with galaxy mass, with the gradients being steeper and the correlation with mass being stronger in late-types. We find, however, that stellar population gradients, for both morphological classifications, have no significant correlation with galaxy environment for all three characterisations of environment. Our results suggest that galaxy mass is the main driver of stellar population gradients in both early and late-type galaxies, and any environmental dependence, if present at all, must be very subtle.

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arXiv2016

The growth of the central region by acquisition of counter-rotating gas in star-forming galaxies

Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (< 1 kpc) to form new stars.

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arXiv2016

Suppressing star formation in quiescent galaxies with supermassive black hole winds

Quiescent galaxies with little or no ongoing star formation dominate the galaxy population above $M_{*}\sim 2 \times 10^{10}~M_{\odot}$, where their numbers have increased by a factor of $\sim25$ since $z\sim2$. Once star formation is initially shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat subsequently accreted gas from stellar mass loss or mergers that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centers of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized gas velocity gradients from which we infer the presence of centrally-driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as $10\%$ of the population at $M_* \sim 2 \times 10^{10}~ M_{\odot}$. In a prototypical example, we calculate that the energy input from the galaxy's low-level active nucleus is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

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arXiv2004

The Disk Mass project; science case for a new PMAS IFU module

We present our Disk Mass project as the main science case for building a new fiber IFU-module for the PMAS spectrograph, currently mounted at the Cassegrain focus of the 3.5m telescope on Calar Alto. Compared to traditional long-slit observations, the large light collecting power of 2-dimensional Integral Field Units dramatically improves the prospects for performing spectroscopy on extended low surface brightness objects with high spectral resolution. This enables us to measure stellar velocity dispersions in the outer disk of normal spiral galaxies. We describe some results from a PMAS pilot study using the existing lenslet array, and provide a basic description of the new fiber IFU-module for PMAS.

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