48 research outputs found
Galaxy Nurseries: Crowdsourced analysis of slitless spectroscopic data
We present the results of Galaxy Nurseries project, which was designed to
enable crowdsourced analysis of slitless spectroscopic data by volunteer
citizen scientists using the Zooniverse online interface. The dataset was
obtained by the WFC3 Infrared Spectroscopic Parallel (WISP) Survey
collaboration and comprises NIR grism (G102 and G141) and direct imaging.
Volunteers were instructed to evaluate indicated spectral features and decide
whether it was a genuine emission line or more likely an artifact. Galaxy
Nurseries was completed in only 40 days, gathering 414,360 classifications from
3003 volunteers for 27,333 putative emission lines. The results of Galaxy
Nurseries demonstrate the feasibility of identifying genuine emission lines in
slitless spectra by citizen scientists. Volunteer responses for each subject
were aggregated to compute , the fraction of volunteers who
classified the corresponding emission line as "Real". To evaluate the accuracy
of volunteer classifications, their aggregated responses were compared with
independent assessments provided by members of the WISP Survey Science Team
(WSST). Overall, there is a broad agreement between the WSST and volunteers'
classifications, although we recognize that robust scientific analyses
typically require samples with higher purity and completeness than raw
volunteer classifications provide. Nonetheless, choosing optimal threshold
values for allows a large fraction of spurious lines to be
vetoed, substantially reducing the timescale for subsequent professional
analysis of the remaining potential lines.Comment: Accepted for publication in Research Notes of the AA
Predicting the redshift 2 Halpha luminosity function using [OIII] emission line galaxies
Upcoming space-based surveys such as Euclid and WFIRST-AFTA plan to measure
Baryonic Acoustic Oscillations (BAOs) in order to study dark energy. These
surveys will use IR slitless grism spectroscopy to measure redshifts of a large
number of galaxies over a significant redshift range. In this paper, we use the
WFC3 Infrared Spectroscopic Parallel Survey (WISP) to estimate the expected
number of Halpha (Ha) emitters observable by these future surveys. WISP is an
ongoing HST slitless spectroscopic survey, covering the 0.8-1.65micron
wavelength range and allowing the detection of Ha emitters up to z~1.5 and
[OIII] emitters to z~2.3. We derive the Ha-[OIII] bivariate line luminosity
function for WISP galaxies at z~1 using a maximum likelihood estimator that
properly accounts for uncertainties in line luminosity measurement, and
demonstrate how it can be used to derive the Ha luminosity function from
exclusively fitting [OIII] data. Using the z~2 [OIII] line luminosity function,
and assuming that the relation between Ha and [OIII] luminosity does not change
significantly over the redshift range, we predict the Ha number counts at z~2 -
the upper end of the redshift range of interest for the future surveys. For the
redshift range 0.7<z<2, we expect ~3000 galaxies/deg^2 for a flux limit of
3x10^{-16} ergs/s/cm^2 (the proposed depth of Euclid galaxy redshift survey)
and ~20,000 galaxies/deg^2 for a flux limit of ~10^{-16} ergs/s/cm^2 (the
baseline depth of WFIRST galaxy redshift survey).Comment: Minor revisions to match accepted ApJ versio
Visions and Violence of Policy: An ethnography of Indigenous Affairs bureaucratic reform in the Northern Territory of Australia
How does a public policy reform become seemingly inevitable? How and why does bureaucratic “common sense” override empirical evidence? What are the overlaps between accountability and corruption? These open-ended questions drive my study of a neglected object of analysis: the well-intentioned people and institutions working within Australia’s Indigenous affairs local government policy arena. In July 2008 the Northern Territory’s local government sector underwent the most sweeping reform of its history, when 53 councils (governing predominantly rural and majority-Indigenous communities) were forcibly amalgamated into eight regional shires. According to the official narrative, the sector had reached a point of crisis: many councils were administratively too small to manage their growing responsibilities. Despite trenchant popular opposition, amalgamations were justified as technically effective, financially efficient -- even morally imperative. Based on a decade of ethnographic research in the Northern Territory including extensive interviews and professional involvement over many years, my thesis moves beyond an empirical evaluation of these events to explore how government actors establish, maintain and self-assess a policy reform. Despite bureaucracy’s claims on rationality and evidence, I argue that factors such morality, routines and aesthetics play more important roles in policy formation than acknowledged. Influenced by the Deleuzian concepts of assemblage and the minor event, I analyse this reform through mundane bureaucratic habits, obscured settler colonial social relations, and near-forgotten events: the rendering of Indigenous totemic art into a corporate logo; a sport and recreation funding agreement as a site of bureaucratic violence; the mobilisation of a created statistic. This perspective invites an alternative to orthodox policy evaluation, whereby the policy cycle is understood ecologically, as a complex assemblage of force, violence and effect. In July 2008 the Northern Territory’s local government sector underwent the most sweeping reform of its history, when 53 councils (governing predominantly rural and majority-Indigenous communities) were forcibly amalgamated into eight regional shires. According to the official narrative, the sector had reached a point of crisis: many councils were administratively too small to manage their growing responsibilities. Despite trenchant popular opposition, amalgamations were justified as technically effective, financially efficient -- even morally imperative. Based on a decade of ethnographic research in the Northern Territory including extensive interviews and professional involvement over many years, my thesis moves beyond an empirical evaluation of these events to explore how government actors establish, maintain and self-assess a policy reform. Despite bureaucracy’s claims on rationality and evidence, I argue that factors such morality, routines and aesthetics play more important roles in policy formation than acknowledged. Influenced by the Deleuzian concepts of assemblage and the minor event, I analyse this reform through mundane bureaucratic habits, obscured settler colonial social relations, and near-forgotten events: the rendering of Indigenous totemic art into a corporate logo; a sport and recreation funding agreement as a site of bureaucratic violence; the mobilisation of a created statistic. This perspective invites an alternative to orthodox policy evaluation, whereby the policy cycle is understood ecologically, as a complex assemblage of force, violence and effect
HST UV Spectroscopy of the Dwarf Starburst Galaxy Pox 186
Studying the galaxies responsible for reionization is often conducted through
local reionization-era analogs; however, many of these local analogs are too
massive to be representative of the low-mass star-forming galaxies that are
thought to play a dominant role in reionization. The local, low-mass dwarf
starburst galaxy Pox 186 is one such system with physical conditions
representative of a reionization-era starburst galaxy. We present deep
ultraviolet (UV) spectroscopy of Pox 186 to study its stellar population and
ionization conditions and to compare these conditions to other local starburst
galaxies. The new Cosmic Origins Spectrograph data are combined with archival
observations to cover 1150-2000 A and allow for an assessment of Pox
186's stellar population, the relative enrichment of C and O, and the escape of
ionizing photons. We detect significant Ly and low-ionization state
absorption features, indicative of previously undetected neutral gas in Pox
186. The C/O relative abundance, log(C/O) = -0.620.02, is consistent with
other low-metallicity dwarf galaxies and suggests a comparable star formation
history in these systems. We compare UV line ratios in Pox 186 to those of
dwarf galaxies and photoionization models, and we find excellent agreement for
the ratios utilizing the intense C III], O III], and double-peaked C IV lines.
However, the UV and optical He II emission is faint and distinguishes Pox 186
from other local starburst dwarf galaxies. We explore mechanisms that could
produce faint He II, which have implications for the low-mass reionization-era
galaxies which may have similar ionization conditions.Comment: 22 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Low Metallicity Galaxies from the Dark Energy Survey
We present a new selection of 358 blue compact dwarf galaxies (BCDs) from
5,000 square degrees in the Dark Energy Survey (DES), and the spectroscopic
follow-up of a subsample of 68 objects. For the subsample of 34 objects with
deep spectra, we measure the metallicity via the direct T method using the
auroral [\oiii] 4363 emission line. These BCDs have average oxygen
abundance of 12+log(O/H)= 7.8, stellar masses between 10 to 10
M and specific SFR between 10 to 10 yr. We
compare the position of our BCDs with the Mass-metallicity (M-Z) and
Luminosity-metallicity (L-Z) relation derived from the Local Volume Legacy
sample. We find the scatter around the M-Z relation is smaller than the scatter
around the L-Z relation. We identify a correlation between the offsets from the
M-Z and L-Z relation that we suggest is due to the contribution of metal-poor
inflows. Finally, we explore the validity of the mass-metallicity-SFR
fundamental plane in the mass range probed by our galaxies. We find that BCDs
with stellar masses smaller than M do not follow the
extrapolation of the fundamental plane. This result suggests that mechanisms
other than the balance between inflows and outflows may be at play in
regulating the position of low mass galaxies in the M-Z-SFR space.Comment: 16 pages, 10 figures, submitted to ApJ, We invite comments from the
communit
HST Grism-derived Forecasts for Future Galaxy Redshift Surveys
The mutually complementary Euclid and Roman galaxy redshift surveys will use Hα- and [O III]-selected emission-line galaxies (ELGs) as tracers of the large-scale structure at 0.9 ≾ z ≾ 1.9 (Hα) and 1.5 ≾ z ≾ 2.7 ([O III]). It is essential to have a reliable and sufficiently precise knowledge of the expected numbers of Hα-emitting galaxies in the survey volume in order to optimize these redshift surveys for the study of dark energy. Additionally, these future samples of ELGs will, like all slitless spectroscopy surveys, be affected by a complex selection function that depends on galaxy size and luminosity, line equivalent width (EW), and redshift errors arising from the misidentification of single ELGs. Focusing on the specifics of the Euclid survey, we combine two slitless spectroscopic WFC3-IR data sets—3D-HST+AGHAST and the WFC3 Infrared Spectroscopic Parallel survey—to construct a Euclid-like sample that covers an area of 0.56 deg² and includes 1277 ELGs. We detect 1091 (~3270 deg⁻²) Hα+[N II]-emitting galaxies in the range 0.9 ≤ z ≤ 1.6 and 162 (~440 deg⁻²) [O III] λ5007 emitters over 1.5 ≤ z ≤ 2.3 with line fluxes ≥2 × 10⁻¹⁶ erg s⁻¹ cm⁻². The median of the Hα+[N II] EW distribution is ~250 Å, and the effective radii of the continuum and Hα+[N II] emission are correlated with a median of ~0.”38 and significant scatter (σ ~ 0.”2–0.”35). Finally, we explore the prevalence of redshift misidentification in future Euclid samples, finding potential contamination rates of ~14%–20% and ~6% down to 2 × 10⁻¹⁶ erg s⁻¹ cm−2 and 6 × 10⁻¹⁷ erg s⁻¹ cm⁻², respectively, although with increased wavelength coverage these percentages drop to nearly zero
HST Grism-derived Forecasts for Future Galaxy Redshift Surveys
The mutually complementary Euclid and Roman galaxy redshift surveys will use
Halpha- and [OIII]-selected emission line galaxies as tracers of the large
scale structure at (Halpha) and ([OIII]). It is essential to have a reliable and sufficiently
precise knowledge of the expected numbers of Halpha-emitting galaxies in the
survey volume in order to optimize these redshift surveys for the study of dark
energy. Additionally, these future samples of emission-line galaxies will, like
all slitless spectroscopy surveys, be affected by a complex selection function
that depends on galaxy size and luminosity, line equivalent width, and redshift
errors arising from the misidentification of single emission-line galaxies.
Focusing on the specifics of the Euclid survey, we combine two slitless
spectroscopic WFC3-IR datasets -- 3D-HST+AGHAST and the WISP survey -- to
construct a Euclid-like sample that covers an area of 0.56 deg and includes
1277 emission line galaxies. We detect 1091 (3270 deg)
Halpha+[NII]-emitting galaxies in the range and 162
(440 deg) [OIII]5007-emitters over
with line fluxes erg s cm. The median of
the Halpha+[NII] equivalent width distribution is 250\r{A}, and the
effective radii of the continuum and Halpha+[NII] emission are correlated with
a median of 0.38" and significant scatter (0.2"0.35").
Finally, we explore the prevalence of redshift misidentification in future
Euclid samples, finding potential contamination rates of 14-20% and
6% down to and erg s
cm, respectively, though with increased wavelength coverage these
percentages drop to nearly zero.Comment: Accepted for publication in ApJ. 27 pages, 17 figures, 3 table
Lyman Continuum Escape Fraction from Low-mass Starbursts at z = 1.3
We present a new constraint on the Lyman continuum (LyC) escape fraction at . We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys Solar Blind Channel on the Hubble Space Telescope, targeting 11 star-forming galaxies at 1.2 190 Å, low stellar mass (M⋆ 3) in the individual galaxies or in the stack in the far-UV images. We place 3σ limits on the relative escape fraction of individual galaxies to be f_(esc,rel) < [0.10-0.22] and a stacked 3σ limit of f_(esc,rel) < 0.07. Measuring various galaxy properties, including stellar mass, dust attenuation, and star formation rate, we show that our measured values fall within the broad range of values covered by the confirmed LyC emitters from the literature. In particular, we compare the distribution of Hα and [O III] EWs of confirmed LyC emitters and non-detections, including the galaxies in this study. Finally, we discuss if a dichotomy seen in the distribution of Hα EWs can perhaps distinguish the LyC emitters from the non-detections
Lyman Continuum Escape Fraction of Star-forming Dwarf Galaxies at z ~ 1
To date, no direct detection of Lyman continuum emission has been measured for intermediate-redshift (z ~ 1) star-forming galaxies. We combine Hubble Space Telescope grism spectroscopy with GALEX UV and ground-based optical imaging to extend the search for escaping Lyman continuum to a large (~600) sample of z ~ 1 low-mass log(M)≃ 9.3 M_☉), moderately star-forming (ψ ≾ 10M_☉ yr^(−1)) galaxies selected initially on Hα emission. The characteristic escape fraction of LyC from star-forming galaxies (SFGs) that populate this parameter space remains weakly constrained by previous surveys, but these faint (sub-Lsstarf) SFGs are assumed to play a significant role in the reionization of neutral hydrogen in the intergalactic medium (IGM) at high redshift z > 6. We do not make an unambiguous detection of escaping LyC radiation from this z ~ 1 sample, individual non-detections to constrain the absolute Lyman continuum escape fraction, f_(esc) 200Å), which are thought to be close analogs of high redshift sources of reionization. For reference, we also present an emissivity-weighted escape fraction that is useful for measuring the general contribution SFGs to the ionizing UV background. In the discussion, we consider the implications of these intermediate redshift constraints for the reionization of hydrogen in the IGM at high (z > 6) redshift. If we assume our z ~ 1 SFGs, for which we measure this emissivity-weighted f_(esc), are analogs to the high redshift sources of reionization, we find it is difficult to reconcile reionization by faint (M}_(UV) ≾-13) SFGs with a low escape fraction (f_(esc) < 3%), with constraints from independent high redshift observations. If f_(esc) evolves with redshift, reionization by SFGs may be consistent with observations from Planck