1,050 research outputs found
Galaxy gas flows inferred from a detailed, spatially resolved metal budget
We use the most extensive integral field spectroscopic map of a local galaxy,
NGC 628, combined with gas and stellar mass surface density maps, to study the
distribution of metals in this galaxy out to 3 effective radii (). At
each galactocentric distance, we compute the metal budget and thus constrain
the mass of metals lost. We find that in the disc about 50% of the metals have
been lost throughout the lifetime of the galaxy. The fraction of metals lost is
higher in the bulge (70%) and decreases towards the outer disc (). In contrast to studies based on the gas kinematics, which are only
sensitive to ongoing outflow events, our metal budget analysis enables us to
infer the average outflow rate during the galaxy lifetime. By using simple
physically motivated models of chemical evolution we can fit the observed metal
budget at most radii with an average outflow loading factor of order unity,
thus clearly demonstrating the importance of outflows in the evolution of disc
galaxies of this mass range (. The observed
gas phase metallicity is higher than expected from the metal budget and
suggests late-time accretion of enriched gas, likely raining onto the disc from
the metal-enriched halo.FB acknowledges support from the United Kingdom Science and Technology Facilities Council. This work makes use of THINGS (‘The Nearby Galaxy Survey’, Walter et al. 2008), HERACLES (the ‘HERA CO line Extragalactic Survey’, Leroy et al. 2009) and PINGS (the ‘PPAK IFS Nearby Galaxy Survey’, Rosales-Ortega et al. 2010). We acknowledge the contribution from the referee in improving the content and the clarity of the paper. We thank Fiorenzo Vincenzo and Francesca Matteucci for their invaluable help in interpreting the vast literature on chemical abundance modelling and nucleosynthetic yields. We also thank Ying-jie Peng for support and discussion on development of his chemical evolution models. We wish to thank Fabian Rosales-Ortega for kindly sharing the PINGS data on NGC 628 and for his encouragement and feedback on the early stages of this work. We thank Matt Auger for useful discussions and healthy skepticism and the participants to the MPIA summer workshop ‘A 3D view on galaxies evolution: from statistics to physics’ for insightful comments.This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv233
Galaxy metallicities depend primarily on stellar mass and molecular gas mass
Aims. We present an analysis of the behaviour of galaxies in a four-dimensional parameter space defined by stellar mass, metallicity, star formation rate, and molecular gas mass. We analyse a combined sample of 227 galaxies that draws from a number of surveys across the redshift range 0 90% of the sample at z ~ 0) and covers >3 decades in stellar mass. Methods. Using principal component analysis, we demonstrate that galaxies in our sample lie on a 2D plane within this 4D parameter space, which is indicative of galaxies that exist in an equilibrium between gas inflow and outflow. Furthermore, we find that the metallicity of galaxies depends only on stellar mass and molecular gas mass. In other words, gas-phase metallicity has a negligible dependence on star formation rate once the correlated effect of molecular gas content is accounted for. Results. The well-known fundamental metallicity relation which describes a close and tight relationship between metallicity and SFR (at fixed stellar mass) is therefore entirely a by-product of the underlying physical relationship with molecular gas mass (through the Schmidt-Kennicutt relation)
Genetic analysis of epidermal growth factor action: assignment of human epidermal growth factor receptor gene to chromosome 7.
Eph receptors and ephrins in the developing chick cerebellum: relationship to sagittal patterning and granule cell migration
Spatiotemporal expression patterns of six members of the Eph gene family (EphA4, EphA3, EphB2, ephrin-B1, ephrin-A2, and ephrin-A5) were characterized immunocytochemically at various stages of chick cerebellar development. EphA4 expression is observed in the cerebellar anlage as early as embryonic day 5 (E5) and continues in the posthatch cerebellum. During the early period of cerebellar development (E3-E8), complementarity is observed between EphA4 and ephrin-A5 expression within the cerebellar-isthmal region. By E8, differential expression of EphA4 in parasagittal Purkinje cell bands is evident, and the expression remains banded in the posthatch cerebellum. Banded expression of the ephrin-A5 ligand complements EphA4 expression during the middle period (E9-E15). During this period, ephrin-A2 and EphA3 are coexpressed in a banded pattern and with variable correlation to EphA4. Variability in the banding expression is observed for EphA4, EphA3, ephrin-A5, and ephrin-A2 across different lobes, and graded complementarity in the expression pattern of EphA3 and ephrin-A5 is observed in the external granular layer between the posterior and anterior lobes. Analysis of Purkinje cell birth date in correlation with Eph-ephrin expression during the middle period reveals that early-born cells express EphA4, whereas late-born cells express ephrin-A5. Finally, EphA4 expression domains are respected by migrating granule cell ribbons, which express both ephrin-B1 and EphB2. These expression patterns suggest multiple roles for the Eph-ephrin system in cerebellar development, including demarcation/enforcement of boundaries of the cerebellar anlage, formation/maintenance of Purkinje cell compartments, and restriction of the early phase of granule cell migration to ribbons
Types of albinism in the black Southern Africa population
Background: Oculocutaneous albinism (OCA) is the most common inherited disorder in Southern African blacks and several types have been described. Molecular techniques, where available, can be used to confirm a clinical diagnosis and the type of OCA, if necessary, and for prenatal diagnosis.Objectives: To investigate and classify the different types of albinism commonly found and to determine the clinical implications for each type.Design: A descriptive survey.Setting: Gauteng province, South Africa, and Lesotho.Subjects: Three groups of subjects with OCA (96 from a genetics clinic, 62 from a dermatology clinic, and 31 from community surveys) from the black African population participated.Main outcome measures: Subjects underwent clinical and/or dermatological examinations and were then classified according to type of OCA.Results: Four forms of OCA were identified: most (82%) subjects had OCA2 (a tyrosinasepositive type) with three sub-types: those without large freckles (ephelides) on exposed areas (named OCA 2a in this study), those with such freckles (named OCA 2b), and those with brown albinism (BOCA); the remainder had red/ rufous albinism, ROCA (OCA 3). The four forms could be distinguished from each other clinically without using molecular genetic testing.Conclusion: The most common types of albinism found in the black population of Southern Africa are OCA 2 and OCA 3. Given the high prevalence of the disorder, together with the high risk of skin cancer, and the recent persecution of affected individuals in certain East African countries, these findings and their clinical implications have significance in terms of both education and awareness for health professionals andlay people caring for those with albinism
Molecular gas as the driver of fundamental galactic relations
There has been much recent work dedicated to exploring secondary correlations in the mass-metallicity relation, with significant dependence on both the SFR (SFR) and Hi content being demonstrated. Previously, a paucity of molecular gas data (combined with sample selection bias) hampered the investigation of any such relation with molecular gas content. In this work, we assemble a sample of 221 galaxies from a variety of surveys in the redshift range 0<z<2, to explore the connection between molecular gas content and metallicity. We explore the effect of gas mass on the mass-metallicity relation, finding that the offset from the relation is negatively correlated against both molecular and total gas mass. We then employ a principle component analysis technique to explore secondary dependences in the mass-metallicity relation, finding that the secondary dependence with gas mass is significantly stronger than with SFR, and as such the underlying ‘fundamental metallicity relation' is between stellar mass, metallicity, and gas mass. In particular, the metallicity dependence on SFR is simply a byproduct of the dependence on the molecular gas content, via the Schmidt-Kennicutt relation. Finally, we note that our principle component analysis finds essentially no connection between gas-phase metallicity and the efficiency of star formatio
ALLSMOG: an APEX Low-redshift Legacy Survey for MOlecular Gas. I - molecular gas scaling relations, and the effect of the CO/H2 conversion factor
We present ALLSMOG, the APEX Low-redshift Legacy Survey for MOlecular Gas.
ALLSMOG is a survey designed to observe the CO(2-1) emission line with the APEX
telescope, in a sample of local galaxies (0.01 < z < 0.03), with stellar masses
in the range 8.5 < log(M*/Msun) < 10. This paper is a data release and initial
analysis of the first two semesters of observations, consisting of 42 galaxies
observed in CO(2-1). By combining these new CO(2-1) emission line data with
archival HI data and SDSS optical spectroscopy, we compile a sample of low-mass
galaxies with well defined molecular gas masses, atomic gas masses, and
gas-phase metallicities. We explore scaling relations of gas fraction and gas
consumption timescale, and test the extent to which our findings are dependent
on a varying CO/H2 conversion factor. We find an increase in the H2/HI mass
ratio with stellar mass which closely matches semi-analytic predictions. We
find a mean molecular gas fraction for ALLSMOG galaxies of MH2/M* = (0.09 -
0.13), which decreases with stellar mass. We measure a mean molecular gas
consumption timescale for ALLSMOG galaxies of 0.4 - 0.7 Gyr. We also confirm
the non-universality of the molecular gas consumption timescale, which varies
(with stellar mass) from ~100 Myr to ~2 Gyr. Importantly, we find that the
trends in the H2/HI mass ratio, gas fraction, and the non-universal molecular
gas consumption timescale are all robust to a range of recent
metallicity-dependent CO/H2 conversion factors.Comment: 25 pages, 15 figures. Accepted for publication in MNRA
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