353 research outputs found
Two Half-Truths Make a Whole? On Bias in Self-Reports and Tracking Data
The pervasive use of mobile information technologies brings new patterns of media usage, but also challenges to the measurement of media exposure. Researchers wishing to, for example, understand the nature of selective exposure on algorithmically driven platforms need to precisely attribute individualsâ exposure to specific content. Prior research has used tracking data to show that survey-based self-reports of media exposure are critically unreliable. So far, however, little effort has been invested into assessing the specific biases of tracking methods themselves. Using data from a multimethod study, we show that tracking data from mobile devices is linked to systematic distortions in self-report biases. Further inherent but unobservable sources of bias, along with potential solutions, are discussed
Spectroscopic Constraints on UV Metal Line Emission at z~6-9: The Nature of Lyman-alpha Emitting Galaxies in the Reionization-Era
Recent studies have revealed intense UV metal emission lines in a modest
sample of z>7 Lyman-alpha emitters, indicating a hard ionizing spectrum is
present. If such high ionization features are shown to be common, it may
indicate that extreme radiation fields play a role in regulating the visibility
of Lyman-alpha in the reionization era. Here we present deep near-infrared
spectra of seven galaxies with Lyman-alpha emission at 5.4<z<8.7 (including a
newly-confirmed lensed galaxy at z=6.031) and three bright z>7 photometric
targets. In nine sources we do not detect UV metal lines. However in the
z=8.683 galaxy EGSY8p7, we detect a 4.6 sigma emission line in the narrow
spectral window expected for NV 1243. The feature is unresolved (FWHM<90 km/s)
and is likely nebular in origin. A deep H-band spectrum of EGSY8p7 reveals
non-detections of CIV, He II, and OIII]. The presence of NV requires a
substantial flux of photons above 77 eV, pointing to a hard ionizing spectrum
powered by an AGN or fast radiative shocks. Regardless of its origin, the
intense radiation field of EGSY8p7 may aid the transmission of Lyman-alpha
through what is likely a partially neutral IGM. With this new detection, five
of thirteen known Lyman-alpha emitters at z>7 have now been shown to have
intense UV line emission, suggesting that extreme radiation fields are
commonplace among the Lyman-alpha population. Future observations with JWST
will eventually clarify the origin of these features and explain their role in
the visibility of Lyman-alpha in the reionization era.Comment: 15 pages, 3 tables and 7 figures. Accepted for publication in MNRA
Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization
We report the discovery of Lyman-alpha emission (Ly) in the bright
galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at
the Keck Observatory. First reported by Roberts-Borsani et al. (2015), it was
selected for spectroscopic observations because of its photometric redshift
(), apparent brightness (H)
and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong
oxygen emission in the [4.5] band. With a total integration of 4.3 hours,
our data reveal an emission line at 11776 {\AA} which we argue is
likely Ly at a redshift , in good
agreement with the photometric estimate. The line was detected independently on
two nights using different slit orientations and its detection significance is
. An overlapping skyline contributes significantly to the
uncertainty on the total line flux although the significance of the detected
line is robust to a variety of skyline-masking procedures. By direct addition
and a Gaussian fit, we estimate a 95\% confidence range of
1.0--2.5 erg s cm, corresponding to a rest-frame
equivalent width of 17--42 {\AA}. EGSY8p7 is the most distant galaxy confirmed
spectroscopically to date, and the third luminous source in the EGS field
beyond with detectable Ly emission viewed at a
time when the intergalactic medium is believed to be fairly neutral. Although
the reionization process was probably patchy, we discuss whether luminous
sources with prominent IRAC color excesses may harbor harder ionizing spectra
than the dominant fainter population thereby creating earlier ionized bubbles.
Further spectroscopic follow-up of such bright sources promises important
insight into the early formation of galaxies.Comment: V3: ApJL accepted; 7 pages, 4 figures, 1 tabl
Lyman-alpha and CIII] Emission in z=7-9 Galaxies: Accelerated Reionization Around Luminous Star Forming Systems?
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous
galaxies at z~7-9 selected to have intense optical line emission by
Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in
two of the four galaxies. Our new MOSFIRE observations confirm that Lyman-alpha
is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1,
confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at
z=7.477, verifying a tentative detection presented in an earlier study. The
ubiquity of Lyman-alpha in this sample is puzzling given that the IGM is likely
significantly neutral over 7<z<9. To investigate this result in more detail, we
have initiated a campaign to target UV metal emission in the four Lyman-alpha
emitters as a probe of both the radiation field and the velocity offset of
Lyman-alpha. Here we present the detection of intense CIII] emission in
EGS-zs8-1, a galaxy from this sample previously shown to have Lyman-alpha at
z=7.73. Photoionization models indicate that an intense radiation field and low
metallicity are required to reproduce the intense CIII] and optical line
emission. We argue that this extreme radiation field is likely to affect the
local environment, increasing the transmission of Lyman-alpha through the
galaxy. Moreover, the centroid of CIII] indicates that Lyman-alpha is
redshifted from the systemic value by 340 km/s. This velocity offset is larger
than that seen in less luminous systems, providing an additional explanation
for the transmission of Lyman-alpha emission through the IGM. Since the
transmission is further enhanced by the likelihood that such systems are also
situated in the densest regions with the largest ionized bubbles, the
visibility of Lyman-alpha at z>7 is expected to be strongly
luminosity-dependent, with the most effective transmission occurring in systems
with intense star formation.Comment: Submitted to MNRAS, 13 pages, 8 figure
Messung von Personalisierung in computervermittelter Kommunikation
Das Ziel personalisierter Online-Angebote ist, Rezipienten bei der Informationssuche zu unterstĂŒtzen. Dabei greifen sie zwangslĂ€ufig in deren Auswahlentscheidungen ein und mĂŒssen deshalb als eigenstĂ€ndiger Einflussfaktor empirisch erschlossen werden. Die dahinterstehenden Algorithmen kommerzieller Anbieter sind fĂŒr die Forschung gröĂtenteils eine intransparente "Black Box". Automatisierte Online-Experimente stellen eine selten eingesetzte Methode dar, die durch systematische Simulation von Nutzerverhalten die Funktionsweise von Personalisierungsalgorithmen ermitteln kann. Der Beitrag diskutiert zunĂ€chst Auswirkungen und Funktionsweise von Personalisierung und stellt daraufhin ein automatisiertes Online-Experiment am Beispiel der Google-Suche dar. Die vorgestellte Methode ermöglicht einen sozialwissenschaftlichen Zugriff auf die Funktionsweise und Inhalte von personalisierten Angeboten und fördert gleichzeitig ValiditĂ€t, Transparenz und Replizierbarkeit von Nutzungsstudien.Personalized web pages are explicitly designed to curate the information available to their users. By definition, they influence users' selectivity and need to be considered as a new factor affecting selection decisions. In most cases, the algorithms that determine recommendations are "black boxes" whose precise functionality remains opaque to researchers. Drawing on a pilot study of Google Search, this chapter argues that the rarely employed automated online experiment represents a promising method for studying "personalization effects". The method presented not only gives researchers access to the effects and contents of personalized web pages, but it also reinforces scientific rigor through higher validity, transparency and replicability of studies on selection behavior
An integrated cryogenic optical modulator
Integrated electrical and photonic circuits (PIC) operating at cryogenic
temperatures are fundamental building blocks required to achieve scalable
quantum computing, and cryogenic computing technologies. Optical interconnects
offer better performance and thermal insulation than electrical wires and are
imperative for true quantum communication. Silicon PICs have matured for room
temperature applications but their cryogenic performance is limited by the
absence of efficient low temperature electro-optic (EO) modulation. While
detectors and lasers perform better at low temperature, cryogenic optical
switching remains an unsolved challenge. Here we demonstrate EO switching and
modulation from room temperature down to 4 K by using the Pockels effect in
integrated barium titanate (BaTiO3)-based devices. We report the nonlinear
optical (NLO) properties of BaTiO3 in a temperature range which has previously
not been explored, showing an effective Pockels coefficient of 200 pm/V at 4 K.
We demonstrate the largest EO bandwidth (30 GHz) of any cryogenic switch to
date, ultra-low-power tuning which is 10^9 times more efficient than thermal
tuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a
missing component for cryogenic PICs. It removes major roadblocks for the
realisation of novel cryogenic-compatible systems in the field of quantum
computing and supercomputing, and for interfacing those systems with the real
world at room-temperature
Slow Evolution of the Specific Star Formation Rate at z>2: The Impact of Dust, Emission Lines, and A Rising Star Formation History
We measure the evolution of the specific star formation rate (sSFR = SFR /
Mstellar) between redshift 4 and 6 to investigate the previous reports of
"constant" sSFR at z>2. We obtain photometry on a large sample of galaxies at
z~4-6 located in the GOODS-S field that have high quality imaging from HST and
Spitzer. We have derived stellar masses and star formation rates (SFRs) through
stellar population modeling of their spectral energy distributions (SEDs). We
estimate the dust extinction from the observed UV colors. In the SED fitting
process we have studied the effects of assuming a star formation history (SFH)
both with constant SFR and one where the SFR rises exponentially with time. The
latter SFH is chosen to match the observed evolution of the UV luminosity
function. We find that neither the mean SFRs nor the mean stellar masses change
significantly when the rising SFR (RSF) model is assumed instead of the
constant SFR model. When focusing on galaxies with Mstar ~ 5x10^9 Msun, we find
that the sSFR evolves weakly with redshift (sSFR(z) \propto (1+z)^(0.6+/-0.1)
Gyr^-1), consistent with previous results and with recent estimates of the sSFR
at z~2-3 using similar assumptions. We have also investigated the impact of
optical emission lines on our results. We estimate that the contribution of
emission lines to the rest-frame optical fluxes is only modest at z~4 and 5 but
it could reach ~50% at z~6. When emission lines of this strength are taken into
account, the sSFR shows somewhat higher values at high redshifts, according to
the relation sSFR(z) \propto (1+z)^(1.0+/-0.1) Gyr^-1, i.e., ~2.3x higher at
z~6 than at z~2. However, the observed evolution is substantially weaker than
that found at z<2 or that expected from current models (which corresponds to
sSFR(z) \propto (1+z)^(2.5) Gyr^-1). -abridged-Comment: 15 pages, 10 figures, 2 tables. Update from v1: after second referee
report, improved (larger) sample at z~
NeutralitĂ€t, Transparenz und Kompetenz: rechtliche Ansatzpunkte fĂŒr eine Neuregulierung des Suchmaschinenmarktes
Die Frage nach den gesellschaftlichen Implikationen der Google-Dienste steht schon lĂ€nger auf der wissenschaftlichen Agenda. Auch die Rechtswissenschaft hat sich dieser Frage in der Vergangenheit bereits angenommen: Ansatz waren dabei hĂ€ufig Fragen des Datenschutzes und des Rechts der Nutzer auf informationelle Selbstbestimmung. Eine Evaluierung der Relevanz des Suchmaschinendienstes als ein zentrales Funktionselement im Internet fĂŒr die öffentliche Meinungsbildung steht allerdings noch aus. Dieser Frage versucht sich der Aufsatz unter RĂŒckgriff auf neue Forschungsergebnisse aus der Kommunikationswissenschaft rechtswissenschaftlich zu nĂ€hern. Danach ist die Suchmaschine wegen ihrer Relevanz fĂŒr die Meinungsvielfaltssicherung in eine gesellschaftliche Verantwortung hineingewachsen, deren ErfĂŒllung der Gesetzgeber aufgrund seiner GewĂ€hrleistungsverantwortung absichern muss. HierfĂŒr werden erste RegulierungsansĂ€tze vorgeschlagen, an denen sich eine Neuregulierung orientieren könnte.Scientific research on the societal implications of Googleâs manifold set of services has a long-standing tradition. Legal scholars have so far mainly focused on data protection, privacy and the "right to informational self-determination". Search enginesâ role in opinion formation, however, has rarely if ever been the subject of a rigorous analysis. This article draws on recent research from mass communication research in order to provide a first assessment of the necessity and possible approaches to search engine regulation from the perspective of media law and plurality
The Rest Frame UV to Optical Colors and SEDs of z~4-7 Galaxies
We use the ultra-deep HUDF09 and the deep ERS data from the HST WFC3/IR
camera, along with the wide area Spitzer/IRAC data from GOODS-S to derive SEDs
of star-forming galaxies from the rest-frame UV to the optical over a wide
luminosity range (M_1500 ~ -21 to M_1500 ~ -18) from z ~ 7 to z ~ 4. The sample
contains ~ 400 z ~ 4, ~ 120 z ~ 5, ~ 60 z ~ 6, and 36 prior z ~ 7 galaxies.
Median stacking enables the first comprehensive study of very faint high-z
galaxies at multiple redshifts (e.g., [3.6] = 27.4 +/- 0.1 AB mag for the
M_1500 ~ -18 sources at z ~ 4). At z ~ 4 our faint median-stacked SEDs reach to
~ 0.06 L*(z=4) and are combined with recently published results at high
luminosity L > L* that extend to M_1500 ~ -23. We use the observed SEDs and
template fits to derive rest frame UV-to-optical colors (U - V) at all
redshifts and luminosities. We find that this color does not vary significantly
with redshift at a fixed luminosity. The UV-to-optical color does show a weak
trend with luminosity, becoming redder at higher luminosities. This is most
likely due to dust. At z >~ 5 we find blue colors [3.6]-[4.5] ~ -0.3 mag that
are most likely due to rest-frame optical emission lines contributing to the
flux in the IRAC filter bandpasses. The scatter across our derived SEDs remains
substantial, but the results are most consistent with a lack of any evolution
in the SEDs with redshift at a given luminosity. The similarity of the SEDs
suggests a self-similar mode of evolution over a timespan from 0.7 Gyr to 1.5
Gyr that encompasses very substantial growth in the stellar mass density in the
universe (from ~ 4x10^6 to ~ 2x10^7 Msun Mpc^-3).Comment: 15 pages, 11 figures, 3 tables, submitted to Ap
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