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R. A. Windhorst

Publications and source records attributed to R. A. Windhorst.

At least 37 records · Page 2Linked to original sources
arXiv2019

An Ultra Deep Field survey with WFIRST

Studying the formation and evolution of galaxies at the earliest cosmic times, and their role in reionization, requires the deepest imaging possible. Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB$\,\sim\,$30, revealing galaxies at the faint end of the LF to $z$$\,\sim\,$9$\,-\,$11 and constraining their role in reionization. However, a key limitation of these fields is their size, only a few arcminutes (less than a Mpc at these redshifts), too small to probe large-scale environments or clustering properties of these galaxies, crucial for advancing our understanding of reionization. Achieving HUDF-quality depth over areas $\sim$100 times larger becomes possible with a mission like the Wide Field Infrared Survey Telescope (WFIRST), a 2.4-m telescope with similar optical properties to HST, with a field of view of $\sim$1000 arcmin$^2$, $\sim$100$\times$ the area of the HST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering $\sim$100$\,-\,$300$\times$ the area of the HUDF, or up to $\sim$1 deg$^2$, to \mAB$\,\sim\,$30, potentially revealing thousands of galaxies and AGN at the faint end of the LF, at or beyond $z$\,$\sim$\,9$\,-\,$10 in the epoch of reionization, and tracing their LSS environments, dramatically increasing the discovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted as input to the Astro2020 Decadal Survey, with this version including an Appendix (which exceeded the Astro2020 page limits), describing how the science drivers for a WFIRST Ultra Deep Field might map into a notional observing program, including the filters used and exposure times needed to achieve these depths.)

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arXiv2018

LSST Observing Strategy White Paper: LSST Observations of WFIRST Deep Fields

The Wide-Field Infrared Survey Telescope (WFIRST) is expected to launch in the mid-2020s. With its wide-field near-infrared (NIR) camera, it will survey the sky to unprecedented detail. As part of normal operations and as the result of multiple expected dedicated surveys, WFIRST will produce several relatively wide-field (tens of square degrees) deep (limiting magnitude of 28 or fainter) fields. In particular, a planned supernova survey is expected to image 3 deep fields in the LSST footprint roughly every 5 days over 2 years. Stacking all data, this survey will produce, over all WFIRST supernova fields in the LSST footprint, ~12-25 deg^2 and ~5-15 deg^2 regions to depths of ~28 mag and ~29 mag, respectively. We suggest LSST undertake mini-surveys that will match the WFIRST cadence and simultaneously observe the supernova survey fields during the 2-year WFIRST supernova survey, achieving a stacked depth similar to that of the WFIRST data. We also suggest additional observations of these same regions throughout the LSST survey to get deep images earlier, have long-term monitoring in the fields, and produce deeper images overall. These fields will provide a legacy for cosmology, extragalactic, and transient/variable science.

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arXiv2018

Deep Extragalactic VIsible Legacy Survey (DEVILS): Motivation, Design and Target Catalogue

The Deep Extragalactic VIsible Legacy Survey (DEVILS) is a large spectroscopic campaign at the Anglo-Australian Telescope (AAT) aimed at bridging the near and distant Universe by producing the highest completeness survey of galaxies and groups at intermediate redshifts ($0.3<z<1.0$). Our sample consists of $\sim$60,000 galaxies to Y$<$21.2mag, over $\sim$6deg$^{2}$ in three well-studied deep extragalactic fields (Cosmic Origins Survey field, COSMOS, Extended Chandra Deep Field South, ECDFS and the X-ray Multi-Mirror Mission Large-Scale Structure region, XMM-LSS - all Large Synoptic Survey Telescope deep-drill fields). This paper presents the broad experimental design of DEVILS. Our target sample has been selected from deep Visible and Infrared Survey Telescope for Astronomy (VISTA) Y-band imaging (VISTA Deep Extragalactic Observations, VIDEO and UltraVISTA), with photometry measured by ProFound. Photometric star/galaxy separation is done on the basis of NIR colours, and has been validated by visual inspection. To maximise our observing efficiency for faint targets we employ a redshift feedback strategy, which continually updates our target lists, feeding back the results from the previous night's observations. We also present an overview of the initial spectroscopic observations undertaken in late 2017 and early 2018.

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arXiv2017

The Lyman Continuum escape fraction of faint galaxies at z~3.3 in the CANDELS/GOODS-North, EGS, and COSMOS fields with LBC

The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the HI ionizing background at z~3. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. We have used ultra-deep U-band imaging (U=30.2mag at 1sigma) by LBC/LBT in the CANDELS/GOODS-North field, as well as deep imaging in COSMOS and EGS fields, in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 L*), while for the faint population (L=0.2L*) the limit to the escape fraction is ~10%. We have computed the contribution of star-forming galaxies to the observed UV background at z~3 and we have found that it is not enough to keep the Universe ionized at these redshifts, unless their escape fraction increases significantly (>10%) at low luminosities (M1500>-19). We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental to measure the Lyman continuum escape fraction down to faint magnitudes (M1500~-16) which are inaccessible with the present instrumentation on blank fields.

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arXiv2016

VLA and ALMA Imaging of Intense, Galaxy-Wide Star Formation in z ~ 2 Galaxies

We present $\simeq$0$.\!\!^{\prime\prime}4$-resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at $z = 1.3-3.0$. These galaxies are selected from sensitive, blank-field surveys of the $2' \times 2'$ Hubble Ultra-Deep Field at $λ= 5$ cm and 1.3 mm using the Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimeter/submillimeter Array (ALMA). They have star-formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at $z \sim 2$. Morphological classification performed on spatially-resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGN), thereby representing a diversity of $z \sim 2$ SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of $4.2 \pm 1.8$ kpc. This provides direct evidence for galaxy-wide star formation in distant, blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M$_{\odot}$yr$^{-1}$kpc$^{-2}$, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGN, which are found to be co-spatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies whose SFRs are $3-8$ times larger, providing a constraint on the characteristic SFR ($\sim300$ M$_{\odot}$yr$^{-1}$) above which a significant population of more compact star-forming galaxies appears to emerge.

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arXiv2016

Do the Most Massive Black Holes at $z=2$ Grow via Major Mergers?

The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here we report on a Hubble Space Telescope study to test this hypothesis for $z=2$ quasars with high super-massive black hole masses ($M_\mathrm{BH}=10^9-10^{10}~M_\odot{}$), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 $F160W$ (rest-frame $V$-band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/non-merger cutoff approach, we recover distortion fractions of $f_\mathrm{m,qso}=0.39\pm{}0.11$ for quasar hosts and $f_\mathrm{m,gal}=0.30\pm{}0.05$ for inactive galaxies (distribution modes, 68% confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higher of $P(f_\mathrm{m,qso}>f_\mathrm{m,gal}) = 0.78$ ($0.78\,σ$), in line with results for lower mass and lower $z$ AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.

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arXiv2014

Early-type galaxies at intermediate redshift observed with HST WFC3: perspectives on recent star-formation

We present an analysis of the stellar populations of 102 visually-selected early-type galaxies (ETGs) with spectroscopic redshifts (0.3 10.5) recently 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 RSF. We conclude that both mechanisms of the quenching of 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 on the relative roles of both of these mechanisms remains an open question.

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arXiv2013

Investigating the Core Morphology-Seyfert Class relationship with Hubble Space Telescope Archival Images of local Seyfert galaxies

The Unified Model of Active Galactic Nuclei (AGN) has provided a successful explanation for the observed diversity of AGN 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 AGN, 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 AGN show that Seyfert class and the "core" (r<~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 (Malkan et al. 1998). We re-establish this empirical relationship in Hubble Space Telescope (HST) 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 parameters methods (the adapted CAS, G-M20), 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.

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arXiv2013

Stellar Populations of Lyman Break Galaxies at z=1-3 in the HST/WFC3 Early Release Science Observations

We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z=1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 sq. arcmin in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z=1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope (beta) is redder than at high redshift (z>3), where LBGs are less dusty; (3) on average, LBGs at z=1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities (0.1L*<~L<~2.5L*), though their median values are similar within 1-sigma uncertainties. This could imply that identical dropout selection technique, at all redshifts, find physically similar galaxies; and (4) stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of ~0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of ~0.90. These relations hold true --- within luminosities probed in this study --- for LBGs from z~1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z~2, but to avoid any selection biases, and for direct comparison with LBGs at z>3, a true Lyman break selection at z~2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

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arXiv2012

The insignificance of major mergers in driving star formation at z~2

We study the significance of major-merger-driven star formation in the early Universe, by quantifying the contribution of this process to the total star formation budget in 80 massive (M* > 10^10 MSun) galaxies at z~2. Employing visually-classified morphologies from rest-frame V-band HST imaging, we find that 55+/-14% of the star formation budget is hosted by non-interacting late-types, with 27+/-8% in major mergers and 18+/-6% in spheroids. Given that a system undergoing a major merger continues to experience star formation driven by other processes at this epoch (e.g. cold accretion, minor mergers), ~27% is an upper limit to the major-merger contribution to star formation activity at this epoch. The ratio of the average specific star formation rate in major mergers to that in the non-interacting late-types is ~2.2:1, suggesting that the enhancement of star formation due to major merging is typically modest, and that just under half the star formation in systems experiencing major mergers is unrelated to the merger itself. Taking this into account, we estimate that the actual major-merger contribution to the star formation budget may be as low as ~15%. While our study does not preclude a major-merger-dominated era in the very early Universe, if the major-merger contribution to star formation does not evolve strongly into larger look-back times, then this process has a relatively insignificant role in driving stellar mass assembly over cosmic time.

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arXiv2012

Newborn spheroids at high redshift: when and how did the dominant, old stars in today's massive galaxies form?

We study ~330 massive (M* > 10^9.5 MSun), newborn spheroidal galaxies (SGs) around the epoch of peak star formation (1 10^10.5 MSun, and an age trend becomes evident in this mass regime: SGs with M* > 10^11.5 MSun are ~2 Gyrs older than their counterparts with M* < 10^10.5 MSun. Nevertheless, a smooth downsizing trend with galaxy mass is not observed, and the large scatter in starburst ages indicate that SGs are not a particularly coeval population. Around half of the blue SGs appear not to drive their star formation via major mergers, and those that have experienced a recent major merger, show only modest enhancements (~40%) in their specific star formation rates. Our empirical study indicates that processes other than major mergers (e.g. violent disk instability driven by cold streams and/or minor mergers) likely play a dominant role in building SGs, and creating a significant fraction of the old stellar populations that dominate today's Universe.

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arXiv2012

A Panchromatic Catalog of Early-Type Galaxies at Intermediate Redshift in the Hubble Space Telescope Wide Field Camera 3 Early Release Science Field

In the first of a series of forthcoming publications, we present a panchromatic catalog of 102 visually-selected early-type galaxies (ETGs) from observations in the Early Release Science (ERS) program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) of the Great Observatories Origins Deep Survey-South (GOODS-S) field. Our ETGs span a large redshift range, 0.35 < z < 1.5, with each redshift spectroscopically-confirmed by previous published surveys of the ERS field. We combine our measured WFC3 ERS and ACS GOODS-S photometry to gain continuous sensitivity from the rest-frame far-UV to near-IR emission for each ETG. The superior spatial resolution of the HST over this panchromatic baseline allows us to classify the ETGs by their small-scale internal structures, as well as their local environment. By fitting stellar population spectral templates to the broad-band photometry of the ETGs, we determine that the average masses of the ETGs are comparable to the characteristic stellar mass of massive galaxies, 11< log(M [Solar]) < 12. By transforming the observed photometry into the GALEX FUV and NUV, Johnson V, and SDSS g' and r' bandpasses we identify a noteworthy diversity in the rest-frame UV-optical colors and find the mean rest-frame (FUV-V)=3.5 and (NUV-V)=3.3, with 1$σ$ standard deviations approximately equal to 1.0. The blue rest-frame UV-optical colors observed for most of the ETGs are evidence for star-formation during the preceding gigayear, but no systems exhibit UV-optical photometry consistent with major recent (<~50 Myr) starbursts. Future publications which address the diversity of stellar populations likely to be present in these ETGs, and the potential mechanisms by which recent star-formation episodes are activated, are discussed.

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arXiv2011

Hubble Space Telescope Observations of Field Ultracool Dwarfs at High Galactic Latitude

We present a sample of 17 newly discovered ultracool dwarf candidates later than ~M8, drawn from 231.90 arcmin2 of {\it Hubble Space Telescope} Wide Field Camera 3 infrared imaging. By comparing the observed number counts for 17.5<J_125<25.5 AB mag to an exponential disk model, we estimate a vertical scale height of z_scl=290 +- 25 (random) +- 30 (systematic) pc for a binarity fraction of f_b=0. While our estimate is roughly consistent with published results, we suggest that the differences can be attributed to sample properties, with the present sample containing far more substellar objects than previous work. We predict the object counts should peak at J_{125}~24 AB mag due to the exponentially-declining number density at the edge of the disc. We conclude by arguing that trend in scale height with spectral type may breakdown for brown dwarfs since they do not settle onto the main sequence.

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arXiv2010

Hubble Space Telescope WFC3 Early Release Science: Emission-Line Galaxies from Infrared Grism Observations

We present grism spectra of emission-line galaxies (ELGs) from 0.6-1.6 microns from the Wide Field Camera 3 on the Hubble Space Telescope. These new infrared grism data augment previous optical Advanced Camera for Surveys G800L 0.6-0.95 micron grism data in GOODS-South from the PEARS program, extending the wavelength covereage well past the G800L red cutoff. The ERS grism field was observed at a depth of 2 orbits per grism, yielding spectra of hundreds of faint objects, a subset of which are presented here. ELGs are studied via the Ha, [OIII], and [OII] emission lines detected in the redshift ranges 0.2 2.

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arXiv2010

UV-dropout Galaxies in the GOODS-South Field from WFC3 Early Release Science Observations

We combine new high sensitivity ultraviolet (UV) imaging from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) with existing deep HST/Advanced Camera for Surveys (ACS) optical images from the Great Observatories Origins Deep Survey (GOODS) program to identify UV-dropouts, which are Lyman break galaxy (LBG) candidates at z~1-3. These new HST/WFC3 observations were taken over 50 sq.arcmin in the GOODS-South field as a part of the Early Release Science program. The uniqueness of these new UV data is that they are observed in 3 UV/optical (WFC3 UVIS) channel filters (F225W, F275W and F336W), which allows us to identify three different sets of UV-dropout samples. We apply Lyman break dropout selection criteria to identify F225W-, F275W- and F336W-dropouts, which are z~1.7, 2.1 and 2.7 LBG candidates, respectively. Our results are as follows: (1) these WFC3 UVIS filters are very reliable in selecting LBGs with z~2.0, which helps to reduce the gap between the well studied z~>3 and z~0 regimes, (2) the combined number counts agrees very well with the observed change in the surface densities as a function of redshift when compared with the higher redshift LBG samples; and (3) the best-fit Schechter function parameters from the rest-frame UV luminosity functions at three different redshifts fit very well with the evolutionary trend of the characteristic absolute magnitude, and the faint-end slope, as a function of redshift. This is the first study to illustrate the usefulness of the WFC3 UVIS channel observations to select z<3 LBGs. The addition of the new WFC3 on the HST has made it possible to uniformly select LBGs from z~1 to z~9, and significantly enhance our understanding of these galaxies using HST sensitivity and resolution.

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arXiv2010

The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program

We present results on the size evolution of passively evolving galaxies at 1 1.5. We identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement spectroscopic redshifts from the literature with photometric redshifts determined from the 15-band photometry from 0.22-8 micron. We determine effective radii from Sersic profile fits to the H-band image using an empirical PSF. We find that size evolution is a strong function of stellar mass, with the most massive (M* ~ 10^11 Msol) galaxies undergoing the most rapid evolution from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha}, we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4 log(M*/10^9 Msol). We briefly discuss the implications of this result for our understanding of the dynamical evolution of the red galaxies.

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arXiv2010

Lifting the Veil of Dust from NGC 0959: The Importance of a Pixel-Based 2D Extinction Correction

We present the results of a study of the late-type spiral galaxy NGC 0959, before and after application of the pixel-based dust extinction correction described in Tamura et al. 2009 (Paper I). Galaxy Evolution Explorer (GALEX) far-UV (FUV) and near-UV (NUV), ground-based Vatican Advanced Technology Telescope (VATT) UBVR, and Spitzer/Infrared Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 micron images are studied through pixel Color-Magnitude Diagrams (pCMDs) and pixel Color-Color Diagrams (pCCDs). We define groups of pixels based on their distribution in a pCCD of (B - 3.6 micron) versus (FUV - U) colors after extinction correction. In the same pCCD, we trace their locations before the extinction correction was applied. This shows that selecting pixel groups is not meaningful when using colors uncorrected for dust. We also trace the distribution of the pixel groups on a pixel coordinate map of the galaxy. We find that the pixel-based (two-dimensional) extinction correction is crucial to reveal the spatial variations in the dominant stellar population, averaged over each resolution element. Different types and mixtures of stellar populations, and galaxy structures such as a previously unrecognized bar, become readily discernible in the extinction-corrected pCCD and as coherent spatial structures in the pixel coordinate map.

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