arXiv subjects

Erika Hamden

Publications and source records attributed to Erika Hamden.

29 records · Page 2Linked to original sources

arXiv2021

End-to-end ground calibration and in-flight performance of the FIREBall-2 instrument

The payload of the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), the second generation of the FIREBall instrument (PI: C. Martin, Caltech), has been calibrated and launched from the NASA Columbia Scientific Balloon Facility (CSBF) in Fort Sumner, NM. FIREBall-2 was launched for the first time on the 22nd September 2018, and the payload performed the very first multi-object acquisition from space using a multi-object slit spectrograph (MOS). This performance-oriented paper presents the calibration and last ground adjustments of FIREBall-2, the in-flight performance assessed based on the flight data, and the predicted instrument's ultimate sensitivity. This analysis predicts that future flights of FIREBall-2 should be able to detect the HI Lyαresonance line in galaxies at z~0.67, but will find it challenging to spatially resolve the circumgalactic medium (CGM).

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arXiv2020

Discovery of an Enormous Ly$α$ nebula in a massive galaxy overdensity at $z=2.3$

Enormous Ly$α$ Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or have targeted known sources such as ultraluminous quasi-stellar-objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Ly$α$ absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at $z=2-3$ (Cai et al. 2016a). In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Ly$α$ nebular luminosity of $L_{\rm{nebula}}=5.1\pm0.1\times10^{44}$ erg s$^{-1}$. Above the 2$σ$ surface brightness limit of SB$_{\rm{Lyα}}= 4.8\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$, this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended \civ\ $\lambda1549$ and \heii\ $\lambda1640$ emission on $\gtrsim30$ kpc scales. Note that the Ly$α$, \heii\ and \civ\ emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of $\approx700 - 1000$ km s$^{-1}$. We argue that this Ly$α$ nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

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arXiv2020

FIREBall-2: The Faint Intergalactic Medium Redshifted Emission Balloon Telescope

The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall) is a mission designed to observe faint emission from the circumgalactic medium of moderate redshift (z~0.7) galaxies for the first time. FIREBall observes a component of galaxies that plays a key role in how galaxies form and evolve, likely contains a significant amount of baryons, and has only recently been observed at higher redshifts in the visible. Here we report on the 2018 flight of the FIREBall-2 Balloon telescope, which occurred on September 22nd, 2018 from Fort Sumner, New Mexico. The flight was the culmination of a complete redesign of the spectrograph from the original FIREBall fiber-fed IFU to a wide-field multi-object spectrograph. The flight was terminated early due to a hole in the balloon, and our original science objectives were not achieved. The overall sensitivity of the instrument and telescope was 90,000 LU, due primarily to increased noise from stray light. We discuss the design of the FIREBall-2 spectrograph, modifications from the original FIREBall payload, and provide an overview of the performance of all systems. We were able to successfully flight test a new pointing control system, a UV-optimized, delta-doped and coated EMCCD, and an aspheric grating. The FIREBall-2 team is rebuilding the payload for another flight attempt in the Fall of 2021, delayed from 2020 due to COVID-19.

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arXiv2020

The FLASHES Survey I: Integral Field Spectroscopy of the CGM around 48 $z=2.3-3.1$ QSOs

We present the pilot study component of the Fluorescent Lyman-Alpha Structures in High-z Environments (FLASHES) Survey; the largest integral-field spectroscopy survey to date of the circumgalactic medium at $z=2.3-3.1$. We observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web Imager (Matuszewski et al. 2010). Extended HI Lyman-$\mathrmα$ emission is discovered around 42/48 of the observed quasars, ranging in projected, flux-weighted radius from 21-71 proper kiloparsecs (pkpc), with 26 nebulae exceeding $100\mathrm{~pkpc}$ in effective diameter. The circularly averaged surface brightness radial profile peaks at a maximum of $\mathrm{1\times 10^{-17}~erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ ($2\times10^{-15}~\mathrm{erg~s^{-1}~cm^{-2}~arcsec^{-2}}$ adjusted for cosmological dimming) and luminosities range from $1.9\times10^{43}~\mathrm{erg~s^{-1}}$ to $-14.1\times10^{43}~\mathrm{erg~s^{-1}}$. The emission appears to have a highly eccentric morphology and a maximum covering factor of $50\%$ ($60\%$ for giant nebulae). On average, the nebular spectra are red-shifted with respect to both the systemic redshift and Ly$α$ peak of the quasar spectrum. The integrated spectra of the nebulae mostly have single or double-peaked line shapes with global dispersions ranging from $167~\mathrm{km~s^{-1}}$ to $690~\mathrm{km~s^{-1}}$, though the individual (Gaussian) components of lines with complex shapes mostly appear to have dispersions $\leq 400$ $\mathrm{km~s^{-1}}$, and the flux-weighted velocity centroids of the lines vary by thousands of $ \mathrm{km~s^{-1}}$ with respect to the systemic QSO redshifts. Finally, the root-mean-square velocities of the nebulae are found to be consistent with gravitational motions expected in dark matter halos of mass $\mathrm{M_h \simeq10^{12.5} M_\odot}$. We compare these results to existing surveys at both higher and lower redshift.

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arXiv2019

Astro2020 APC White Paper: The Early Career Perspective on the Coming Decade, Astrophysics Career Paths, and the Decadal Survey Process

In response to the need for the Astro2020 Decadal Survey to explicitly engage early career astronomers, the National Academies of Sciences, Engineering, and Medicine hosted the Early Career Astronomer and Astrophysicist Focus Session (ECFS) on October 8-9, 2018 under the auspices of Committee of Astronomy and Astrophysics. The meeting was attended by fifty six pre-tenure faculty, research scientists, postdoctoral scholars, and senior graduate students, as well as eight former decadal survey committee members, who acted as facilitators. The event was designed to educate early career astronomers about the decadal survey process, to solicit their feedback on the role that early career astronomers should play in Astro2020, and to provide a forum for the discussion of a wide range of topics regarding the astrophysics career path. This white paper presents highlights and themes that emerged during two days of discussion. In Section 1, we discuss concerns that emerged regarding the coming decade and the astrophysics career path, as well as specific recommendations from participants regarding how to address them. We have organized these concerns and suggestions into five broad themes. These include (sequentially): (1) adequately training astronomers in the statistical and computational techniques necessary in an era of "big data", (2) responses to the growth of collaborations and telescopes, (3) concerns about the adequacy of graduate and postdoctoral training, (4) the need for improvements in equity and inclusion in astronomy, and (5) smoothing and facilitating transitions between early career stages. Section 2 is focused on ideas regarding the decadal survey itself, including: incorporating early career voices, ensuring diverse input from a variety of stakeholders, and successfully and broadly disseminating the results of the survey.

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arXiv2019

Multi-Filament Inflows Fueling Young Star Forming Galaxies

Theory suggests that there are two primary modes of accretion through which dark matter halos acquire the gas to form and fuel galaxies, hot and cold mode accretion. In cold mode accretion, gas streams along cosmic web filaments to the center of the halo, allowing for the efficient delivery of star-forming fuel. Recently, two QSO-illuminated HI Lyman alpha (Lyα) emitting objects were reported to have properties of cold, rotating structures (Martin et al. 2015, Martin et al. 2016). However, the spatial and spectral resolution available was insufficient to constrain radial flows associated with connecting filaments. With the Keck Cosmic Web Imager (KCWI) we now have eight times the spatial resolution, permitting the detection of these in-spiraling flows. In order to detect these inflows, we introduce a suite of models which incorporate zonal radial flows, demonstrate their performance on a numerical simulation that exhibits coldflow accretion, and show that they are an excellent match to KCWI velocity maps of two Lyα emitters observed around high-redshift quasars. These Multi-Filament Inflow models kinematically isolate zones of radial inflow that correspond to extended filamentary emission. The derived gas flux and inflow path is sufficient to fuel the inferred central galaxy star formation rate and angular momentum. Thus, our kinematic emission maps provide strong evidence for the inflow of gas from the cosmic web building galaxies at the peak of star formation.

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arXiv2019

Understanding the circumgalactic medium is critical for understanding galaxy evolution

Galaxies evolve under the influence of gas flows between their interstellar medium and their surrounding gaseous halos known as the circumgalactic medium (CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a key role in the long cycles of accretion, feedback, and recycling of gas that drive star formation. In order to fully understand the physical processes at work within galaxies, it is therefore essential to have a firm understanding of the composition, structure, kinematics, thermodynamics, and evolution of the CGM. In this white paper we outline connections between the CGM and galactic star formation histories, internal kinematics, chemical evolution, quenching, satellite evolution, dark matter halo occupation, and the reionization of the larger-scale intergalactic medium in light of the advances that will be made on these topics in the 2020s. We argue that, in the next decade, fundamental progress on all of these major issues depends critically on improved empirical characterization and theoretical understanding of the CGM. In particular, we discuss how future advances in spatially-resolved CGM observations at high spectral resolution, broader characterization of the CGM across galaxy mass and redshift, and expected breakthroughs in cosmological hydrodynamic simulations will help resolve these major problems in galaxy evolution.

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arXiv2018

Keck/Palomar Cosmic Web Imagers (KCWI/PCWI) Reveal an Enormous Ly$α$ Nebula in an Extremely Overdense QSO Pair Field at $z=2.45$

Enormous Ly$α$ nebulae (ELANe) represent the extrema of Ly$α$ nebulosities. They have detected extents of $>200$ kpc in Ly$α$ and Ly$α$ luminosities $>10^{44}$ erg s$^{-1}$. The ELAN population is an ideal laboratory to study the interactions between galaxies and the intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes. The current sample size of ELANe is still very small, and the few $z\approx2$ ELANe discovered to date are all associated with local overdensities of active galactic nuclei (AGNs). Inspired by these results, we have initiated a survey of ELANe associated with QSO pairs using the Palomar and Keck Cosmic Web Imagers (PCWI/KCWI). In this letter, we present our first result: the discovery of ELAN0101+0201 associated with a QSO pair at $z=2.45$. Our PCWI discovery data shows that, above a 2-$σ$ surface brightness of $1.2\times10^{-17}$ \sbunit, the end-to-end size of ELAN0101+0201 is $\gtrsim 232$ kpc. We have conducted follow-up observations using KCWI, resolving multiple Ly$α$ emitting sources within the rectangular field-of-view of $\approx 130\times165$ projected kpc$^2$, and obtaining their emission line profiles at high signal-to-noise ratios. Combining both KCWI and PCWI, our observations confirm that ELAN0101+0201 resides in an extremely overdense environment. Our observations further support that a large amount of cool ($T\sim10^4$K) gas could exist in massive halos (M$\gtrsim10^{13}$M$_\odot$) at $z\approx2$. Future observations on a larger sample of similar systems will provide statistics of how cool gas is distributed in massive overdensities at high-redshift and strongly constrain the evolution of the intracluster medium (ICM).

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arXiv2017

High Efficiency UV/Optical/NIR Detectors for Large Aperture Telescopes and UV Explorer Missions: Development of and Field Observations with Delta-doped Arrays

A number of exciting concepts are under development for Flagship, Probe class, Explorer class, and Suborbital class NASA missions in the ultraviolet/optical spectral ranges. These missions will depend on high performance silicon detector arrays being delivered affordably and in high numbers. In a focused effort we have advanced delta-doping technology to high throughput and high yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. As part of this technology advancement and in preparation for upcoming missions, we have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. In this paper, we present recent data and innovations from the Advanced Detectors and Systems program at JPL, including two-dimensional doping technology; our end-to-end post-fabrication processing of high performance UV/Optical/NIR arrays; and advanced coatings for detectors and optical elements. Additionally, we present examples of past, in-progress, and planned observations and deployments of delta-doped arrays.

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arXiv2013

The Diffuse Galactic Far-Ultraviolet Sky

We present an all sky map of the diffuse Galactic far ultraviolet (1344-1786 Angstroms) background using GALEX data, covering 65% of the sky with 11.79 arcmin square pixels. We investigate the dependence of the background on Galactic coordinates, finding that a standard cosecant model of intensity is not a valid fit. Furthermore, we compare our map to Galactic all sky maps of 100 micron emission, N_HI column, and H-alpha intensity. We measure a consistent low level FUV intensity at zero-points for other Galactic quantities, indicating a 300 CU non-scattered isotropic component to the diffuse FUV. There is also a linear relationship between FUV and 100 micron emission below 100 micron values of 8 MJy/sr. We find a similar linear relationship between FUV and NHI below 10^21 square cm. The relationship between FUV and H-alpha intensity has no such constant cutoff. For all Galactic quantities, the slope of the linear portion of the relationship decreases with Galactic latitude. A modified cosecant model, taking into account dust scattering asymmetry and albedo, is able to accurately fit the diffuse FUV at latitudes above 20 degrees. The best fit model indicates an albedo, a, of 0.62 +- 0.04 and a scattering asymmetry function, g, of 0.78 +- 0.05. Deviations from the model fit may indicate regions of excess FUV emission from fluorescence or shock fronts, while low latitude regions with depressed FUV emission are likely the result of self-shielding dusty clouds.

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arXiv2011

Silicon Detector Arrays with Absolute Quantum Efficiency over 50% in the Far Ultraviolet for Single Photon Counting Applications

We have used Molecular Beam Epitaxy (MBE)-based delta doping technology to demonstrate near 100% internal quantum efficiency (QE) on silicon electron-multiplied Charge Coupled Devices (EMCCDs) for single photon counting detection applications. Furthermore, we have used precision techniques for depositing antireflection (AR) coatings by employing Atomic Layer Deposition (ALD) and demonstrated over 50% external QE in the far and near-ultraviolet in megapixel arrays. We have demonstrated that other device parameters such as dark current are unchanged after these processes. In this paper, we report on these results and briefly discuss the techniques and processes employed.

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