Matching Items (15)

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Early-Type Galaxies at Intermediate Redshift Observed With Hubble Space Telescope WFC3: Perspectives on Recent Star Formation

Description

We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science

We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one- and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (∼40%) are likely to have experienced a minor (fYC ≲ 10% of stellar mass) burst of recent (tYC ≲ 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 1010.5M☼) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.

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Created

Date Created
  • 2014-12-01

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A Guide to Large Binocular Telescope Data Reduction

Description

Abstract Located in southeastern Arizona, the Large Binocular Telescope is a great local resource for ASU astronomy/cosmology researchers. As a ground-based observatory, the Large Binocular Telescope can effectively provide deep,

Abstract Located in southeastern Arizona, the Large Binocular Telescope is a great local resource for ASU astronomy/cosmology researchers. As a ground-based observatory, the Large Binocular Telescope can effectively provide deep, complementary observations of science fields in the wavelength range of 3,500 to 10,000 Angstroms. This gives scientists a lot of opportunity for various science projects, which can lead to massive amounts of observations being taken by research schools with ties to the LBT. Such is the case with ASU, which has obtained over 30 hours of data in just the SDT Uspec filter on board the Large Binocular Camera (Blue) and much more time in other filters observing longer wavelengths. Because of this, there is a huge need for establishing a system that will allow the reduction of raw astronomical images from the LBT to be quickly, but accurately. This manuscript serves as a presentation of the work done over the 2015-2016 school year to establish a pipeline for reducing LBT raw science images as well as a guide for future undergraduates and graduates to reduce data on their own.

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Created

Date Created
  • 2016-05

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SED Analysis of 43 Spectroscopically Confirmed Galaxies at z ~ 6 to Constrain Possible Relationships between UV Slope, Model Dust Attenuation, and Escape Fraction

Description

The reionization of the Universe is thought to have completed by redshift z~5.5. To probe this era, galaxy observations in the Subaru Deep Field (SDF) have identified more than 100

The reionization of the Universe is thought to have completed by redshift z~5.5. To probe this era, galaxy observations in the Subaru Deep Field (SDF) have identified more than 100 galaxies at z~6, many spectroscopically confirmed through follow-up observations. Using available optical/IR data, we model with CIGALE the spectral energy distributions (SEDs) of 43 SDF galaxies, including newly acquired data from the UKIRT WFCAM K-band for seven previously studied objects. In particular, modeling deep IR photometry is sensitive to the galaxy's Lyman continuum (LyC) escape fraction (fesc). We find the median implied fesc value as ~0.4+/-0.1 (mean error). Significant uncertainties in data and fitting result in a large range of fesc for individual objects, but analysis suggests that fesc is likely high enough for galaxies to finish reionization by z~6. More importantly, we find trends between the CIGALE UV slope b, fesc, and dust extinction E(B-V): for a given E(B-V), b appear steeper by ~0.4 than at z=0. Lower fesc values appear to be associated with bluer b and lower E(B-V), but only weakly. This suggests that LyC could have escaped through holes with sufficiently wide opening angles surrounding the ISM from outflows of supernovae and/or weak AGN to escape, but resulting in a large range of implied fesc values depending on the orientation of each galaxy. The current HST, Spitzer and ground-based photometric and model errors for the 43 galaxies are large, so IR spectroscopic observations with the James Webb Space Telescope are needed to better constrain this possibility.

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Created

Date Created
  • 2021-05

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The Potential Use for Strong Gravitational Lensing in the Detection of Dark Matter

Description

Both strong and weak gravitational lensing allow astronomers to calculate the mass distribution of the foreground lens by analysis of the distortion of the lensed light. This process is currently

Both strong and weak gravitational lensing allow astronomers to calculate the mass distribution of the foreground lens by analysis of the distortion of the lensed light. This process is currently the most precise way to quantify the presence of dark matter in galaxies. In addition, strong gravitational lensing allows astronomers to observe directly the light from the background source, as it will be both magnified in brightness and easier to resolve. Current computer models can essentially "remove" the foreground galaxy/galaxies to isolate and reconstruct an image of the background source with a resolution greater than that observed without lensing. Both the measurement of dark matter within galaxies and the direct observation of lensed galaxies are goals for this project. This was done using LENSTOOL, a software package chosen for the project, and originally designed to perform such calculations efficiently. While neither goal was met in its entirety, this paper reflects the results of this project throughout the course of the past year.

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Created

Date Created
  • 2018-05

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Studying Spectral Index of Radio Galaxies with LOFAR

Description

Radio astronomy is a subfield in astronomy that deals with objects emitting frequencies around 10 MHz to 100 GHz. The Low Frequency Array (LOFAR) is a array of radio antennas

Radio astronomy is a subfield in astronomy that deals with objects emitting frequencies around 10 MHz to 100 GHz. The Low Frequency Array (LOFAR) is a array of radio antennas in Europe that can reach very low frequencies, roughly between 10-240 MHz. Our project was to image and clean a field from LOFAR. The data was a 10 degree square in the sky centered at a right ascension of 10:19:34.608 and a declination +49.36.52.482. It was observed for 600 seconds at 141 MHz. To clean the field, we had to flag and remove any stations that were not responding. Using a program called FACTOR, we cleaned the image and reduced the residuals. Next we checked the validity of our sources. We checked positional offsets for our sources using the TGSS survey at 150 MHz, and corrected the declination of our LOFAR sources by a factor of 0.0002 degrees. We also fixed the LOFAR fluxes by a factor of 1.15. After this systematic check, we calculated the spectral index of our sources using the FIRST survey at 1435 MHz. We plotted this spectral index against LOFAR flux as well as redshift of the sources, and compared these to literature.

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Agent

Created

Date Created
  • 2017-05

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INVESTIGATING THE CORE MORPHOLOGY-SEYFERT CLASS RELATIONSHIP WITH HUBBLE SPACE TELESCOPE ARCHIVAL IMAGES OF LOCAL SEYFERT GALAXIES

Description

The unified model of active galactic nuclei (AGNs) has provided a successful explanation for the observed diversity of AGNs in the local universe. However, recent analysis of multi-wavelength spectral and

The unified model of active galactic nuclei (AGNs) has provided a successful explanation for the observed diversity of AGNs in the local universe. However, recent analysis of multi-wavelength spectral and image data suggests that the unified model is only a partial theory of AGNs, and may need to be augmented to remain consistent with all observations. Recent studies using high spatial resolution ground-and space-based observations of local AGNs show that Seyfert class and the "core" (r less than or similar to 1 kpc) host-galaxy morphology are correlated. Currently, this relationship has only been established qualitatively, by visual inspection of the core morphologies of low-redshift (z < 0.035) Seyfert host galaxies. We re-establish this empirical relationship in Hubble Space Telescope optical imaging by visual inspection of a catalog of 85 local (D < 63 Mpc) Seyfert galaxies. We also attempt to re-establish the core morphology-Seyfert class relationship using an automated, non-parametric technique that combines both existing classification parameter methods (the adapted CAS and G-M-20) and a new method which implements the Source Extractor software for feature detection in unsharp-mask images. This new method is designed explicitly to detect dust features in the images. We use our automated approach to classify the morphology of the AGN cores and determine that Sy2 galaxies visually appear, on average, to have more dust features than Sy1. With the exception of this "dustiness" however, we do not measure a strong correlation between the dust morphology and the Seyfert class of the host galaxy using quantitative techniques. We discuss the implications of these results in the context of the unified model.

Contributors

Created

Date Created
  • 2013-10-28

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Attempting to Produce Helium White Dwarfs From Low-Metallicity Solar Mass Stars

Description

I examine the effects of metallicity on solar mass stellar evolution, trying to replicate a previous result in Windhorst et.al., 2018, in which a zer metallicity solar mass star did

I examine the effects of metallicity on solar mass stellar evolution, trying to replicate a previous result in Windhorst et.al., 2018, in which a zer metallicity solar mass star did not reach the AGB, and thus may turn into a helium white dwarf. In trying to replicate this result, I used the M.E.S.A. stellar evolution code and was unable to reproduce this result. While M.E.S.A has undergone several updates since the previous result was obtained, more current evidence suggests that this may have been a one-time occurrence, as no helium white dwarfs were produced for low-metallicity models. Nonetheless, interesting results were obtained, including a lowest metallicity value for which CNO burning does not significantly contribute during the main sequence, 1 −10 Z , which produces noticeable effects on post main sequence evolution. All models are run with no rotation, one solar mass, and a series of MESA parameters kept constant, with the only exception being metallicity. Any metallicity value listed as Nd −10 is an absolute mass fraction, and Z is relative to solar metallicity, 2d*10 −2 .

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Agent

Created

Date Created
  • 2019-12

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Correlating Galactic Magnetic Fields with Regions of Dense Star Formation using LOFAR and CALIFA

Description

I test the hypothesis that galactic magnetic fields originate from regions of dense
star formation (Dahlem et al. 2006) by comparing maps of 120-240 MHz synchrotron emission and hydrogen alpha

I test the hypothesis that galactic magnetic fields originate from regions of dense
star formation (Dahlem et al. 2006) by comparing maps of 120-240 MHz synchrotron emission and hydrogen alpha (Hα) emission of the tidally-interacting, edge-on, barred spiral galaxy UGC 9665. Synchrotron emission traces magnetic field strength to a rough first order, while Hα emission traces recent massive star formation. UGC 9665 was selected because it was included in the LOw Frequency ARray (LOFAR) TwoMetre Sky Survey (LoTSS; Shimwell et al. (2017)) as well as the Calar Alto Legacy Integral Field Area Survey (CALIFA; Sanchez et al. (2012)). I generated vertical intensity profiles at several distances along the disk from the galactic center for synchrotron emission and Hα in order to measure how the intensity of each falls off with distance from the midplane. In addition to correlating the vertical profiles to see if there is a relationship between star formation and magnetic field strength, I fit the LOFAR vertical profiles to characteristic Gaussian and exponential functions given by Dumke et al. (1995). Fitting these equations have been shown to be good indicators of the main mode of cosmic ray transport, whether it is advection (exponential fit) or diffusion (Gaussian fit) (Heesen et al. 2016). Cosmic rays originate from supernova,
and core collapse supernovae occur in star forming regions, which also produce
advective winds, so I test the correlation between star-forming regions and advective regions as predicted by the Heesen et al. (2016) method. Similar studies should be conducted on different galaxies in the future in order to further test these hypotheses and how well LOFAR and CALIFA complement each other, which will be made possible by the full release of the LOFAR Two-Metre Sky Survey (LoTSS) (Shimwell et al. 2017).

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Agent

Created

Date Created
  • 2019-05

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The study of astronomical transients in the infrared

Description

Several key, open questions in astrophysics can be tackled by searching for and

mining large datasets for transient phenomena. The evolution of massive stars and

compact objects can be studied over cosmic

Several key, open questions in astrophysics can be tackled by searching for and

mining large datasets for transient phenomena. The evolution of massive stars and

compact objects can be studied over cosmic time by identifying supernovae (SNe) and

gamma-ray bursts (GRBs) in other galaxies and determining their redshifts. Modeling

GRBs and their afterglows to probe the jets of GRBs can shed light on the emission

mechanism, rate, and energetics of these events.

In Chapter 1, I discuss the current state of astronomical transient study, including

sources of interest, instrumentation, and data reduction techniques, with a focus

on work in the infrared. In Chapter 2, I present original work published in the

Proceedings of the Astronomical Society of the Pacific, testing InGaAs infrared

detectors for astronomical use (Strausbaugh, Jackson, and Butler 2018); highlights of

this work include observing the exoplanet transit of HD189773B, and detecting the

nearby supernova SN2016adj with an InGaAs detector mounted on a small telescope

at ASU. In Chapter 3, I discuss my work on GRB jets published in the Astrophysical

Journal Letters, highlighting the interesting case of GRB 160625B (Strausbaugh et al.

2019), where I interpret a late-time bump in the GRB afterglow lightcurve as evidence

for a bright-edged jet. In Chapter 4, I present a look back at previous years of

RATIR (Re-ionization And Transient Infra-Red Camera) data, with an emphasis on

the efficiency of following up GRBs detected by the Fermi Space Telescope, before

some final remarks and brief discussion of future work in Chapter 5.

Contributors

Agent

Created

Date Created
  • 2019