arXiv subjects

Moire K. M. Prescott

Publications and source records attributed to Moire K. M. Prescott.

At least 19 recordsLinked to original sources

arXiv2025

A Galactic Self-Portrait: Density Structure and Integrated Properties of the Milky Way Disk

The evolution history of the Milky Way disk is imprinted in the ages, positions, and chemical compositions of individual stars. In this study, we derive the intrinsic density distribution of different stellar populations using the final data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A total of 203,197 red giant branch stars are used to sort the stellar disk ($R \leq 20$ kpc) into sub-populations of metallicity ($Δ$[M/H]$= 0.1$ dex), age ($Δ\log(\frac{\textrm{age}}{\textrm{yr}})= 0.1$), and $α$-element abundances ([$α$/M]). We fit the present-day structural parameters and density distribution of each stellar sub-population after correcting for the survey selection function. The low-$α$ disk is characterized by longer scale lengths and shorter scale heights, and is best fit by a broken exponential radial profile for each population. The high-$α$ disk is characterized by shorter scale lengths and larger scale heights, and is generally well-approximated by a single exponential radial profile. These results are applied to produce new estimates of the integrated properties of the Milky Way from early times to the present day. We measure the total stellar mass of the disk to be $5.27^{+0.2}_{-1.5} \times 10^{10}$ M$_\odot$ and the average mass-weighted scale length is $R_{d} = 2.37 \pm 0.2$ kpc. The Milky Way's present-day color of $(g-r) = 0.72 \pm 0.02$ is consistent with the classification of a red spiral galaxy, although it has only been in the "green valley" region of the galaxy color-mass diagram for the last $\sim 3$ Gyr.

astro-ph.GA↗

arXiv2024

SAUNAS II: Discovery of Cross-shaped X-ray Emission and a Rotating Circumnuclear Disk in the Supermassive S0 Galaxy NGC 5084

Combining Chandra, ALMA, EVLA, and Hubble Space Telescope archival data and newly acquired APO/DIS spectroscopy, we detect a double-lobed 17~kpc X-ray emission with plumes oriented approximately perpendicular and parallel to the galactic plane of the massive lenticular galaxy NGC\,5084 at 0.3--2.0~keV. We detect a highly inclined ($i=71.2^{+1.8\circ}_{-1.7}$), molecular circumnuclear disk ($D=304^{+10}_{-11}$ pc) in the core of the galaxy rotating (V$^{\rm (2-1) CO}_{\rm rot}=242.7^{+9.6}_{-6.4}$ km s$^{-1}$) in a direction perpendicular to that of the galactic disk, implying a total mass of $\log_{10}\left( \frac{M_{\rm BH}}{M_{\odot}} \right) = 7.66^{+0.21}_{-0.15}$ for NGC\,5084's supermassive black hole. Archival EVLA radio observations at 6 cm and 20 cm reveal two symmetric radio lobes aligned with the galactic plane, extending to a distance of $\overline{R}=4.6\pm0.6$ kpc from the core, oriented with the polar axis of the circumnuclear disk. The spectral energy distribution lacks strong emission lines in the optical range. Three formation scenarios are considered to explain these multi-wavelength archival observations: 1) AGN re-orientation caused by accretion of surrounding material, 2) AGN-driven hot gas outflow directed along the galactic minor axis, or 3) a starburst / supernovae driven outflow at the core of the galaxy. This discovery is enabled by new imaging analysis tools including \SAUNAS\ (Selective Amplification of Ultra Noisy Astronomical Signal), demonstrating the abundance of information still to be exploited in the vast and growing astronomical archives.

astro-ph.GA↗

arXiv2024

Prevalence of a growth mindset among introductory astronomy students

While many previous studies have indicated that encouraging a growth mindset can improve student learning outcomes, this conclusion's applicability to college-level astronomy classrooms remains poorly understood owing to the variation in students' overall and domain-specific learning attitudes. To address this, we surveyed undergraduate students in an introductory astronomy class about their attitudes towards learning astronomy over the course of five semesters. Overall, students felt an affinity for astronomy, felt moderately competent, perceived astronomy to be intermediate in terms of difficulty, and agreed strongly with standard statements reflecting a "growth mindset," i.e., the belief that intelligence is malleable rather than fixed from birth. Their responses were stable over the course of the semester and did not appear to depend strongly on student demographics. The unexpected start of the COVID-19 pandemic and the associated shift to all-virtual learning correlated with a drop in their affinity for astronomy, a small decrease in their perceived competence, and an increase in the perceived difficulty of the topic. Their overall learning mindset showed negligible change during this time, emphasizing the stability of their belief in a growth mindset as compared to other measured learning attitudes. However, more nuanced questions about their behaviors and interpretations in the classroom, about how they felt "in the moment", and about what factors were most important for their success in the class revealed significantly lower alignment with a growth mindset. This suggests that while introductory astronomy students may believe that they have a growth mindset, this mindset is not necessarily reflected in their self-reported classroom behaviors or measured responses to actual learning challenges.

physics.ed-ph↗

arXiv2024

Signatures of AGN feedback modes: A Green Bean Galaxy with 150 kpc jet-induced radio emission

Jetted Active Galactic Nuclei (AGN) hosting extended photoionized nebulae provide us with a unique view of the timescales associated with AGN activity. Here, we present a new Green Bean galaxy (RGB1) at $z=0.304458\pm0.000007$ with large scale jet-induced radio emission. The Spectral Energy Distributions (SEDs) of the radio components show steep spectral indices ($α=-0.85$ to $-0.92$ for the extended regions, and $α=-1.02$ for the faint radio core), and spectral age modeling of the extended radio emission indicates that the lobes are $>$6 Myrs old. It is unclear whether the jet is active, or remnant with an off-time of 2-3 Myr. Several detached clouds lie around the host galaxy up to 37.8 kpc away from the nucleus, and their ionization profile indicates a decline ($\sim$2 dex) in the AGN ionizing photon production over the past $\sim$0.15 Myr. Furthermore, we measure a blue shift for one of the clouds that is spatially coincident with the path of the radio jet. The cloud is likely illuminated by the photoionizing AGN, and potentially underwent an interaction with the relativistic jet. Our multiwavelength analysis suggests that RGB1 was in a phase of jet production prior to the radiatively efficient accretion phase traced by the detached cloud emission. It is unclear whether RGB1 transitioned into a low-excitation radio galaxy or an inactive galaxy over the past $\sim$0.15 Myr, or whether the extended radio and optical emission trace distinct accretion phases that occurred in succession.

astro-ph.GA↗

arXiv2023

Brighter and More Massive Galaxies in the Vicinity of Lyman-alpha Nebulae

It has been well established in the local universe that galaxy properties differ based on the large-scale environment in which they reside. As luminous Lyman-alpha nebulae have been shown to trace overdense environments at z~2-3, comparing the properties of galaxies within Lyman-alpha nebulae systems to those in the field can provide insight into how and when locally-observed trends between galaxy properties and environment emerged. Six Lyman-alpha nebulae were discovered at z~2.3 in a blind search of the GOODS-S extragalactic field, a region also covered by the 3D-HST spectroscopic survey. Utilizing 3D-HST data, we identified 86 galaxies in the vicinity of these nebulae and used statistical tests to compare their physical properties to galaxies elsewhere in the field. Galaxies lying within 320 proper kpc of a Lyman-alpha nebula are roughly half a magnitude brighter than those in the field, with higher stellar masses, higher star formation rates, and larger effective radii. Even when considering the effects of sample incompleteness, our study suggests that galaxies in overdensities at z~2.3 traced by Lyman-alpha nebulae are being influenced by their environment. Furthermore, Lyman-alpha nebula-associated galaxies lie on the same main sequence of star formation as field galaxies, but have a larger proportion of high-mass galaxies, consistent with the idea that galaxy evolution is accelerated in rich environments. Expanded surveys for Lyman-alpha nebulae in other deep extragalactic fields and galaxy spectroscopic follow-up with JWST will better constrain the demographics of Lyman-alpha nebula-associated galaxies.

astro-ph.GA↗

arXiv2022

Lyman-Alpha Escape from Low-Mass, Compact, High-Redshift Galaxies

We investigate the effects of stellar populations and sizes on Ly$α$ escape in 27 spectroscopically confirmed and 35 photometric Lyman-Alpha Emitters (LAEs) at z $\approx$ 2.65 in seven fields of the Boötes region of the NOAO Deep Wide-Field Survey. We use deep $HST$/WFC3 imaging to supplement ground-based observations and infer key galaxy properties. Compared to typical star-forming galaxies (SFGs) at similar redshifts, the LAEs are less massive ($M_{\star} \approx 10^{7} - 10^{9}~M_{\odot}$), younger (ages $\lesssim$ 1 Gyr), smaller ($r_{e} <$ 1 kpc), less dust-attenuated (E(B$-$V) $\le$ 0.26 mag), but have comparable star-formation-rates (SFRs $\approx 1 - 100~M_{\odot} {\rm yr^{-1}}$). Some of the LAEs in the sample may be very young galaxies having low nebular metallicities (${\rm Z_{neb} \lesssim 0.2 Z_{\odot}}$) and/or high ionization parameters ($\log{(\rm U)} \gtrsim -2.4$). Motivated by previous studies, we examine the effects of the concentration of star formation and gravitational potential on Ly$α$ escape, by computing star-formation-rate surface density, $Σ_{\rm SFR}$ and specific star-formation-rate surface density, $Σ_{\rm sSFR}$. For a given $Σ_{\rm SFR}$, the Ly$α$ escape fraction is higher for LAEs with lower stellar masses. LAEs have higher $Σ_{\rm sSFR}$ on average compared to SFGs. Our results suggest that compact star formation in a low gravitational potential yields conditions amenable to the escape of Ly$α$ photons. These results have important implications for the physics of Ly$α$ radiative transfer and for the type of galaxies that may contribute significantly to cosmic reionization.

astro-ph.GA↗

arXiv2022

Using Multiple Emission Line Ratios to Constrain the Slope of the Dust Attenuation Law

We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of eleven galaxies with existing ground-based Balmer H$α$ and H$β$ measurements from slit spectra, plus space-based grism constraints on Paschen-$β$. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best-fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-$β$/H$α$ ratios driving these results. We find that galaxies with high Paschen-$β$/H$α$ ratios may be explained by slightly sub-unity covering fractions ($>$97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at $z\approx0.3-2$, enabling uniform constraints on the optical-infrared dust attenuation law and its intrinsic variation.

astro-ph.GA↗

arXiv2021

Mapping the Morphology and Kinematics of a Lyman-alpha-selected Nebula at z=3.15 with MUSE

Recent wide-field integral field spectroscopy has revealed the detailed properties of high redshift Lyman-alpha (Lya) nebulae, most often targeted due to the presence of an active galactic nucleus (AGN). Here, we use VLT/MUSE to resolve the morphology and kinematics of a nebula initially identified due to strong Lya emission at $z\sim3.2$ (LABn06; Nilsson et al. 2006). Our observations reveal a two-lobed Lya nebula, at least $\sim$173 pkpc in diameter, with a light-weighted centroid near a mid-infrared source (within $\approx$17.2 pkpc) that appears to host an obscured AGN. The Lya emission near the AGN is also coincident in velocity with the kinematic center of the nebula, suggesting that the nebula is both morphologically and kinematically centered on the AGN. Compared to AGN-selected Lya nebulae, the surface brightness profile of this nebula follows a typical exponential profile at large radii ($>$25 pkpc), although at small radii, the profile shows an unusual dip at the location of the AGN. The kinematics and asymmetry are similar to, and the CIV and HeII upper limits are consistent with other AGN-powered Lya nebulae. Double-peaked and asymmetric line profiles suggest that Lya resonant scattering may be important in this nebula. These results support the picture of the AGN being responsible for powering a Lya nebula that is oriented roughly in the plane of the sky. Further observations will explore whether the central surface brightness depression is indicative of either an unusual gas or dust distribution or variation in the ionizing output of the AGN over time.

astro-ph.GA↗

arXiv2019

Understanding Lyman-alpha Nebulae at Low Redshift I: The Sizes, Powering, and Kinematics of "Green Bean" Galaxies

A new but rare sample of spatially extended emission line nebulae, nicknamed "Green Beans", was discovered at z~0.3 thanks to strong [OIII] emission, and subsequently shown to be local cousins of the Lyman-alpha (Lya) nebulae found at high redshift. Here we use follow-up APO/DIS spectroscopy to better understand how these low redshift Lya nebulae compare to other populations of strong emission line sources. Our spectroscopic data show that low-z Lya nebulae have AGN-like emission line ratios, relatively narrow line widths (FWHM<1000 km s^{-1}), and emission line kinematics resembling those of Type 2 AGN at the same redshift, confirming that they are powered by Type 2 AGN with typical ionizing continua. While low-z Lya nebulae are larger and less concentrated than compact, star-forming Green Pea galaxies, we find that they resemble typical Type 2 AGN in terms of r-band concentration and size. Based on this pilot study, low-z Lya nebulae appear to be a subset of Type 2 AGN with bluer optical continua and high [OIII] equivalent widths but with comparable sizes and similar [OIII] kinematics. These characteristics may simply reflect the fact that low-z Lya nebulae are drawn from the high luminosity end of the Type 2 AGN distribution, with higher nuclear activity driving higher [OIII] equivalent widths and more central star formation leading to bluer optical continua. Deeper spectroscopic follow-up of the full sample will shed further light on these issues and on the relationship between these low-z Lya nebulae and the Lya nebula population at high redshift.

astro-ph.GA↗

arXiv2017

The Diversity of Diffuse Ly$α$ Nebulae around Star-Forming Galaxies at High Redshift

We report the detection of diffuse Ly$α$ emission, or Ly$α$ halos (LAHs), around star-forming galaxies at $z\approx3.78$ and $2.66$ in the NOAO Deep Wide-Field Survey Boötes field. Our samples consist of a total of $\sim$1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Ly$α$ images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Ly$α$ radial profile into a compact galaxy-like and an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Ly$α$ luminosities, but not on Ly$α$ equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Ly$α$ emitters ($M_{\rm UV} \gtrsim -21$), exhibit LAH sizes of 5$\,-\,6\,$kpc. However, the most UV- or Ly$α$-luminous galaxies have more extended halos with scale-lengths of 7$\,-\,9\,$kpc. The stacked Ly$α$ radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. On the other hand, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, HI column density, and outflow velocity) change with halo mass and/or star-formation rates.

astro-ph.GA↗

arXiv2016

Mapping the Polarization of the Radio-Loud Ly$α$ Nebula B3 J2330+3927

Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] > 10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions at z ~ 2--5. The origin of the Lya emission remains unknown, but recent theoretical work suggests that measuring the polarization might discriminate among powering mechanisms. Here we present the first narrowband, imaging polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya emission peak and its radio lobes align roughly with the blob's major axis. With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya + continuum) polarization in a grid of circular apertures of radius 0.6" (4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine apertures and achieving strong upper-limits (as low as 2%) elsewhere. P increases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The detections are distributed asymmetrically, roughly along the nebula's major axis. The polarization angles theta are mostly perpendicular to this axis. Comparing the Lya flux to that of the continuum, and conservatively assuming that the continuum is highly polarized (20-100%) and aligned with the total polarization, we place lower limits on the polarization of the Lya emission P(Lya) ranging from no significant polarization at ~5 kpc from the blob center to ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization detections occur more often along the blob's major axis.

astro-ph.GA↗

arXiv2015

Overturning the Case for Gravitational Powering in the Prototypical Cooling Lyman-alpha Nebula

The Nilsson et al. (2006) Lyman-alpha nebula has often been cited as the most plausible example of a Lyman-alpha nebula powered by gravitational cooling. In this paper, we bring together new data from the Hubble Space Telescope and the Herschel Space Observatory as well as comparisons to recent theoretical simulations in order to revisit the questions of the local environment and most likely power source for the Lyman-alpha nebula. In contrast to previous results, we find that this Lyman-alpha nebula is associated with 6 nearby galaxies and an obscured AGN that is offset by $\sim$4"$\approx$30 kpc from the Lyman-alpha peak. The local region is overdense relative to the field, by a factor of $\sim$10, and at low surface brightness levels the Lyman-alpha emission appears to encircle the position of the obscured AGN, highly suggestive of a physical association. At the same time, we confirm that there is no compact continuum source located within $\sim$2-3"$\approx$15-23 kpc of the Lyman-alpha peak. Since the latest cold accretion simulations predict that the brightest Lyman-alpha emission will be coincident with a central growing galaxy, we conclude that this is actually a strong argument against, rather than for, the idea that the nebula is gravitationally-powered. While we may be seeing gas within cosmic filaments, this gas is primarily being lit up, not by gravitational energy, but due to illumination from a nearby buried AGN.

astro-ph.GA↗

arXiv2014

Spatially Resolved Gas Kinematics within a Ly$α$ Nebula: Evidence for Large-scale Rotation

We use spatially extended measurements of Ly$α$ as well as less optically thick emission lines from an $\approx$80 kpc Ly$α$ nebula at $z\approx1.67$ to assess the role of resonant scattering and to disentangle kinematic signatures from Ly$α$ radiative transfer effects. We find that the Ly$α$, CIV, HeII, and CIII] emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. First, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the Ly$α$ photons are produced in situ instead of being resonantly scattered from a central source. Second, we see low kinematic offsets between Ly$α$ and the less optically thick HeII line ($\sim$100-200 km s$^{-1}$), providing further support for the argument that the Ly$α$ and other emission lines are all being produced within the spatially extended gas. Finally, the full velocity field of the system shows coherent velocity shear in all emission lines: $\approx$500 km s$^{-1}$ over the central $\approx$50 kpc of the nebula. The kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. These observations suggest that the Ly$α$ nebula represents accreting material that is illuminated by an offset, hidden AGN or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of M(<R=20 kpc)$\sim3\times10^{11}$ $M_{\odot}$, this system may represent the early formation of a large Milky Way mass galaxy or galaxy group.

astro-ph.GA↗

arXiv2014

Pinpointing the Molecular Gas within a Lyman Alpha Blob at z ~ 2.7

We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emission are detected at the location of a strong MIPS source that is offset by ~1.5" from the Ly-alpha peak. Neither of these emission components is resolved with the 1.7" beam, showing that the gas and dust are confined to within ~7kpc from this galaxy. No millimeter source is found at the location of the Ly-alpha peak, ruling out a central compact source of star formation as the power source for the Ly-alpha emission. Combined with a spatially-resolved spectrum of Ly-alpha and HeII, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Ly-alpha profile is symmetric and its line center agrees with that of CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Ly-alpha emission. In the region near the Ly-alpha peak, the gas is slowly receding (~100km/s) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, I_CO(5-4)/I_CO(3-2)=0.97+/-0.21. This line ratio is lower than the average values found in high-z SMGs and QSOs, but consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity.

astro-ph.GA↗

arXiv2013

On the Automated and Objective Detection of Emission Lines in Faint-Object Spectroscopy

Modern spectroscopic surveys produce large spectroscopic databases, generally with sizes well beyond the scope of manual investigation. The need arises, therefore, for an automated line detection method with objective indicators for detection significance. In this paper, we present an automated and objective method for emission line detection in spectroscopic surveys and apply this technique to 1574 spectra, obtained with the Hectospec spectrograph on the MMT Observatory (MMTO), to detect Lyman alpha emitters near z ~ 2.7. The basic idea is to generate on-source (signal plus noise) and off-source (noise only) mock observations using Monte Carlo simulations, and calculate completeness and reliability values, (C, R), for each simulated signal. By comparing the detections from real data with the Monte Carlo results, we assign the completeness and reliability values to each real detection. From 1574 spectra, we obtain 881 raw detections and, by removing low reliability detections, we finalize 649 detections from an automated pipeline. Most of high completeness and reliability detections, (C, R) ~ (1.0, 1.0), are robust detections when visually inspected; the low C and R detections are also marginal on visual inspection. This method at detecting faint sources is dependent on the accuracy of the sky subtraction.

astro-ph.IM↗

arXiv2012

A Successful Broad-band Survey for Giant Lya Nebulae II: Spectroscopic Confirmation

Using a systematic broad-band search technique, we have carried out a survey for large Lya nebulae (or Lya "blobs") at 2<z<3 within 8.5 square degrees of the NOAO Deep Wide-Field Survey (NDWFS) Bootes field, corresponding to a total survey comoving volume of ~10^8 h_70^-3 Mpc^3. Here, we present our spectroscopic observations of candidate giant Lya nebulae. Of 26 candidates targeted, 5 were confirmed to have Lya emission at 1.7<z<2.7, four of which were new discoveries. The confirmed Lya nebulae span a range of Lya equivalent widths, colors, sizes, and line ratios, and most show spatially-extended continuum emission. The remaining candidates did not reveal any strong emission lines, but instead exhibit featureless, diffuse, blue continuum spectra. Their nature remains mysterious, but we speculate that some of these might be Lya nebulae lying within the redshift desert (i.e., 1.2<z<1.6). Our spectroscopic follow-up confirms the power of using deep broad-band imaging to search for the bright end of the Lya nebula population across enormous comoving volumes.

astro-ph.CO↗

arXiv2012

Resolving the Galaxies within a Giant Lya Nebula: Witnessing the Formation of a Galaxy Group?

Detailed analysis of the substructure of Lya nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high resolution HST imaging of a Lya nebula at z~2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially-extended emission. The system is characterized by (a) a population of compact, low luminosity (~0.1 L*) sources --- 17 primarily young, small (Re~1-2 kpc), disky galaxies including an obscured AGN --- that are all substantially offset (>20 kpc) from the line-emitting nebula; (b) the lack of a central galaxy at or near the peak of the Lya emission; and (c) several nearly coincident, spatially extended emission components --- Lya, HeII, and UV continuum --- that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Lya nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of 4). These observations provide the first estimate of the luminosity function of galaxies within an individual Lya nebula system, and suggest that large Lya nebulae may be the seeds of galaxy groups or low-mass clusters.

astro-ph.CO↗

arXiv2012

A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection

Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2<z<3 within deep broad-band imaging and have carried out a survey of the 9.4 square degree NOAO Deep Wide-Field Survey (NDWFS) Bootes field. With a total survey comoving volume of ~10^8 h^-3_70 Mpc^3, this is the largest volume survey for Lya nebulae ever undertaken. In this first paper in the series, we present the details of the survey design and a systematically-selected sample of 79 candidates, which includes one previously discovered Lya nebula.

astro-ph.CO↗