217 research outputs found
Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes
We investigate the roles of two classes of quenching mechanisms for central
and satellite galaxies in the SDSS (): those involving the halo and
those involving the formation of a compact centre. For central galaxies with
inner compactness ,
the quenched fraction is strongly correlated with
with only weak halo mass dependence. However, at higher and lower
, sSFR is a strong function of and mostly
independent of . In other words, divides galaxies into those with high sSFR
below and low sSFR above this range. In both the upper and lower regimes,
increasing shifts the entire sSFR distribtuion to lower sSFR
without a qualitative change in shape. This is true even at fixed , but
varying at fixed adds no quenching information. Most of the
quenched centrals with are dense (), suggesting compaction-related
quenching maintained by halo-related quenching. However, 21% are diffuse,
indicating only halo quenching. For satellite galaxies in the outskirts of
halos, quenching is a strong function of compactness and a weak function of
host . In the inner halo, dominates quenching, with
of the satellites being quenched once . This regional effect is greatest for the least massive
satellites. As demonstrated via semi-analytic modelling with simple
prescriptions for quenching, the observed correlations can be explained if
quenching due to central compactness is rapid while quenching due to halo mass
is slow.Comment: 16 pages, 11 figures, MNRAS accepte
Supermassive black holes as the regulators of star formation in central galaxies
We present a relationship between the black hole mass, stellar mass, and star
formation rate of a diverse group of 91 galaxies with dynamically-measured
black hole masses. For our sample of galaxies with a variety of morphologies
and other galactic properties, we find that the specific star formation rate is
a smoothly decreasing function of the ratio between black hole mass and stellar
mass, or what we call the specific black hole mass. In order to explain this
relation, we propose a physical framework where the gradual suppression of a
galaxy's star formation activity results from the adjustment to an increase in
specific black hole mass and, accordingly, an increase in the amount of
heating. From this framework, it follows that at least some galaxies with
intermediate specific black hole masses are in a steady state of partial
quiescence with intermediate specific star formation rates, implying that both
transitioning and steady-state galaxies live within this region known as the
"green valley." With respect to galaxy formation models, our results present an
important diagnostic with which to test various prescriptions of black hole
feedback and its effects on star formation activity.Comment: 15 pages, 4 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Translating neuroscience: When is the use of clickers effective for student learning?
Objective: Teaching large content heavy classes presents a challenge to faculty in any discipline.In nursing education, particularly pharmacotherapeutics, student learning is critical to patient safety.Therefore, effective teaching practices are a must.But, there is a lack of education literature that connects the neuroscience of why a specific method such as using the technology of personal response systems (PRS) contributes to student learning.This study discusses the use of action research to evaluate the effectiveness of the use of personal response systems (PRS) or “clickers” in an undergraduate nursing pharmacology course, using knowledge of neuroscience to interpret the results.
Methods:Action research was used to apply Neuro-semantic Language Learning Theory to the use of clickers in a nursing pharmatherapeutics course.Action research design allowed for the continuity of assessment and reflection by the faculty.
Results:Outcomes were measures quantitatively using ATI (Assessment Technologies Institute) test scores pre- and post-intervention.ATI scores improved with the use of clickers.Qualitative student comments indicated satisfaction with the use of clickers to improve learning.Neuroscience and learning theory are used to explain the results of the study.
Conclusion:Clickers by themselves do not necessarily create better learning, but thoughtful, purposeful integration of the technology, using techniques based on neuroscience elicit higher order thinking and provides deeper conceptual learning
Two conditions for galaxy quenching: compact centres and massive haloes
We investigate the roles of two classes of quenching mechanisms for central and satellite galaxies in the Sloan Digital Sky Survey (z1011.8 M⊙ are dense (Σ1 kpc>109 M⊙ kpc−2), suggesting compaction-related quenching maintained by halo-related quenching. However, 21 per cent are diffuse, indicating only halo quenching. For satellite galaxies in the outskirts of haloes, quenching is a strong function of compactness and a weak function of host Mh. In the inner halo, Mh dominates quenching, with ∼90 per cent of the satellites being quenched once Mh>1013 M⊙. This regional effect is greatest for the least massive satellites. As demonstrated via semi-analytic modelling with simple prescriptions for quenching, the observed correlations can be explained if quenching due to central compactness is rapid while quenching due to halo mass is slo
Interacting galaxies in the IllustrisTNG simulations - III. (The rarity of) quenching in post-merger galaxies
Galaxy mergers are traditionally one of the favoured mechanisms for the transformation of spiral galaxies to spheroids and for quenching star formation. To test this paradigm in the context of modern cosmological simulations, we use the IllustrisTNG simulation to investigate the impact of individual merger events on quenching star formation [i.e. star formation rate (SFR) at least 3σ below the star-forming main sequence] within 500 Myr after the coalescence phase. The rate of quenching amongst recently merged galaxies is compared with a control sample that is matched in redshift, stellar mass, SFR, black hole mass, and environment. We find quenching to be uncommon among the descendants of post-merger galaxies, with only ∼5 per cent of galaxies quenching within 500 Myr after the merger. Despite this low absolute rate, we find that quenching occurs in post-mergers at twice the rate of the control galaxies. The fraction of quenched post-merger descendants 1.5 Gyr after the merger become statistically indistinguishable from that of non-post-mergers, suggesting that mergers could speed up the quenching process in those post-mergers whose progenitors had physical conditions able to sustain effective active galactic nuclei (AGN) kinetic feedback, thus capable of removing gas from galaxies. Our results indicate that although quenching does not commonly occur promptly after coalescence, mergers none the less do promote the cessation of star formation in some post-mergers. We find that, in IllustrisTNG, it is the implementation of the AGN kinetic feedback that is responsible for quenching post-mergers, as well as non-post-merger controls. As a result of the released kinetic energy, galaxies experience gas loss and eventually they will quench. Galaxies with an initially low gas fraction show a preferable pre-disposition towards quenching. The primary distinguishing factor between quenched and star-forming galaxies is gas fraction, with a sharp boundary at fgas ~ 0.1 in TNG
What shapes a galaxy? - Unraveling the role of mass, environment and star formation in forming galactic structure
We investigate the dependence of galaxy structure on a variety of galactic
and environmental parameters for ~500,000 galaxies at z<0.2, taken from the
Sloan Digital Sky Survey data release 7 (SDSS-DR7). We utilise bulge-to-total
stellar mass ratio, (B/T)_*, as the primary indicator of galactic structure,
which circumvents issues of morphological dependence on waveband. We rank
galaxy and environmental parameters in terms of how predictive they are of
galaxy structure, using an artificial neural network approach. We find that
distance from the star forming main sequence (Delta_SFR), followed by stellar
mass (M_*), are the most closely connected parameters to (B/T)_*, and are
significantly more predictive of galaxy structure than global star formation
rate (SFR), or any environmental metric considered (for both central and
satellite galaxies). Additionally, we make a detailed comparison to the
Illustris hydrodynamical simulation and the LGalaxies semi-analytic model. In
both simulations, we find a significant lack of bulge-dominated galaxies at a
fixed stellar mass, compared to the SDSS. This result highlights a potentially
serious problem in contemporary models of galaxy evolution.Comment: Accepted to MNRAS. 31 pages, 15 figure
AGN Feedback in SDSS-IV MaNGA: AGNs have Suppressed Central Star Formation Rates
Despite the importance of feedback from active galactic nuclei (AGNs) in
models of galaxy evolution, observational constraints on the influence of AGN
feedback on star formation remain weak. To this end, we have compared the star
formation trends of 279 low-redshift AGN galaxies with 558 inactive control
galaxies using integral field unit spectroscopy from the SDSS-IV MaNGA survey.
With a Gaussian process-based methodology, we reconstruct nonparametric star
formation histories in spatially resolved spaxels covering the face of each
galaxy. Based on galaxy-wide star formation rates (SFRs) alone, we find no
obvious signatures of AGN feedback. However, the AGN galaxies have
significantly suppressed central (kiloparsec-scale) SFRs, lying up to a factor
of below those of the control galaxies, providing direct observational
evidence of AGN feedback suppressing star formation. The suppression of central
SFRs in the AGN galaxies began in the central regions Gyr ago
(redshift ), taking place over a few gigayears. A small subset of
the AGN galaxies were rapidly driven to quiescence shortly before being
observed (in the last Myr), potentially indicating instances of
AGN-driven feedback. More frequently, however, star formation continues in the
AGN galaxies, with suppression primarily in the central regions. This is
suggestive of a picture in which integrated (Gyr-timescale) AGN feedback can
significantly affect central star formation, but may be inefficient in driving
galaxy-wide quenching in low-redshift galaxies, instead leaving them in the
green valley.Comment: 22 pages, 15 figures. Accepted for publication in Ap
Dependence of Galaxy Quenching on Halo Mass and Distance from its Centre
We study the dependence of star-formation quenching on galaxy mass and
environment, in the SDSS (z~0.1) and the AEGIS (z~1). It is crucial that we
define quenching by low star-formation rate rather than by red colour, given
that one third of the red galaxies are star forming. We address stellar mass
M*, halo mass Mh, density over the nearest N neighbours deltaN, and distance to
the halo centre D. The fraction of quenched galaxies appears more strongly
correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites
quenching also depends on D. We present the M*-Mh relation for centrals at z~1.
At z~1, the dependence of quenching on M* at fixed Mh is somewhat more
pronounced than at z~0, but the quenched fraction is low (10%) and the haloes
are less massive. For satellites, M*-dependent quenching is noticeable at high
D, suggesting a quenching dependence on sub-halo mass for recently captured
satellites. At small D, where satellites likely fell in more than a few Gyr
ago, quenching strongly depends on Mh, and not on M*. The Mh-dependence of
quenching is consistent with theoretical wisdom where virial shock heating in
massive haloes shuts down accretion and triggers ram-pressure stripping,
causing quenching. The interpretation of deltaN is complicated by the fact that
it depends on the number of observed group members compared to N, motivating
the use of D as a better measure of local environment.Comment: 23 pages, 13 figures, accepted by MNRA
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