scholarly journals Heterogeneity of inverted calcium ii H:K ratio cluster galaxies

2019 ◽  
Vol 490 (1) ◽  
pp. 455-466
Author(s):  
K A Pimbblet ◽  
J P Crossett ◽  
A Fraser-McKelvie
Keyword(s):  
Selection Criteria ◽  
Stellar Population ◽  
Spiral Galaxies ◽  
Simple Relationship ◽  
Lower Mass ◽  
Field Sample ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Passive Sample ◽  
Selection Of

ABSTRACT The ratio of calcium ii H plus Hϵ to calcium ii K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O ii] beyond having a high value for strong [O ii] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O ii] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more ‘pure’ passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed.

scholarly journals The nature of submillimetre and highly star-forming galaxies in the EAGLE simulation

2019 ◽  
Vol 488 (2) ◽  
pp. 2440-2454 ◽  
Author(s):  
Stuart McAlpine ◽  
Ian Smail ◽  
Richard G Bower ◽  
A M Swinbank ◽  
James W Trayford ◽  
...  
Keyword(s):  
Reasonable Agreement ◽  
Lower Mass ◽  
Redshift Distribution ◽  
Gas Reservoir ◽  
Massive Galaxies ◽  
Star Forming ◽  
Hydrodynamical Simulation ◽  
Galaxy Population ◽  
Gas Fractions ◽  
Selection Of

ABSTRACT We exploit EAGLE, a cosmological hydrodynamical simulation, to reproduce the selection of the observed submillimetre (submm) galaxy population by selecting the model galaxies at z ≥ 1 with mock submm fluxes $S_{850\, \mu \mathrm{m}}$ ≥ 1 mJy. We find a reasonable agreement between the model galaxies within this sample and the properties of the observed submm population, such as their star formation rates (SFRs) at z < 3, redshift distribution, and many integrated galaxy properties. We find that the median redshift of the $S_{850\, \mu \mathrm{m}}$ ≥ 1 mJy model population is z ≈ 2.5, and that they are massive galaxies (M* ∼ 1011 M⊙) with high dust masses (Mdust ∼ 108 M⊙), gas fractions (fgas ≈ 50 per cent), and SFRs ($\dot{M}_* \approx 100$ M⊙ yr−1). In addition, we find that they have major and minor merger fractions similar to the general population, suggesting that mergers are not the sole driver of the high SFRs in the model submm galaxies. Instead, the $S_{850\, \mu \mathrm{m}}$ ≥ 1 mJy model galaxies yield high SFRs primarily because they maintain a significant gas reservoir as a result of hosting an undermassive black hole relative to comparably massive galaxies. Not all ‘highly star-forming’ ($\dot{M}_* \ge 80$ M⊙ yr−1) eagle galaxies have submm fluxes $S_{850\, \mu \mathrm{m}}$ ≥ 1 mJy. We investigate the nature of these highly star-forming ‘Submm-Faint’ galaxies (i.e. $\dot{M}_* \ge 80$ M⊙ yr−1 but $S_{850\, \mu \mathrm{m}}$ < 1 mJy) and find that they are similar to the model submm galaxies, being gas rich and hosting undermassive black holes. However, they are also typically at higher redshifts (z > 4) and are lower mass (M* ∼ 1010 M⊙). These typically higher redshift galaxies show stronger evidence for having been triggered by major mergers, and critically, they are likely missed by most current submm surveys due to their higher dust temperatures and lower dust masses.

scholarly journals Stellar Population Synthesis of Star-forming Clumps in Galaxy Pairs and Non-interacting Spiral Galaxies

2018 ◽  
Vol 234 (2) ◽  
pp. 35 ◽  
Author(s):  
Javier Zaragoza-Cardiel ◽  
Beverly J. Smith ◽  
Margarita Rosado ◽  
John E. Beckman ◽  
Theodoros Bitsakis ◽  
...  
Keyword(s):  
Stellar Population ◽  
Spiral Galaxies ◽  
Population Synthesis ◽  
Star Forming ◽  
Stellar Population Synthesis

scholarly journals Luminosity functions of cluster galaxies

2018 ◽  
Vol 618 ◽  
pp. A180 ◽  
Author(s):  
Roberto De Propris ◽  
Malcolm N. Bremer ◽  
Steven Phillipps
Keyword(s):  
Luminosity Function ◽  
Velocity Dispersion ◽  
Lower Mass ◽  
X Ray ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Luminosity Functions ◽  
Blue Galaxies ◽  
Cluster Properties ◽  
Good Agreement

We derive NUV luminosity functions for 6471 NUV detected galaxies in 28 0.02 < z < 0.08 clusters and consider their dependence on cluster properties. We consider optically red and blue galaxies and explore how their NUV LFs vary in several cluster subsamples, selected to best show the influence of environment. Our composite LF is well fit by the Schechter form with M*NUV = −18.98 ± 0.07 and α = −1.87 ± 0.03 in good agreement with values for the Coma centre and the Shapley supercluster, but with a steeper slope and brighter L* than in Virgo. The steep slope is due to the contribution of massive quiescent galaxies that are faint in the NUV. There are significant differences in the NUV LFs for clusters having low and high X-ray luminosities and for sparse and dense clusters, though none are particularly well fitted by the Schechter form, making a physical interpretation of the parameters difficult. When splitting clusters into two subsamples by X-ray luminosity, the ratio of low to high NUV luminosity galaxies is higher in the high X-ray luminosity subsample (i.e., the luminosity function is steeper across the sampled luminosity range). In subsamples split by surface density, when characterised by Schechter functions the dense clusters have an M* about a magnitude fainter than that of the sparse clusters and α is steeper (−1.9 vs. −1.6, respectively). The differences in the data appear to be driven by changes in the LF of blue (star-forming) galaxies. This appears to be related to interactions with the cluster gas. For the blue galaxies alone, the luminosity distributions indicate that for high LX and high velocity dispersion cluster subsamples (i.e., the higher mass clusters), there are relatively fewer high UV luminosity galaxies (or correspondingly a relative excess of low UV luminosity galaxies) in comparison the lower mass cluster subsamples.

scholarly journals Circumnuclear Star Formation in Spiral Galaxies from HST Images: NGC 4314

2002 ◽  
Vol 207 ◽  
pp. 708-710
Author(s):  
Cláudia Winge ◽  
Miriani G. Pastoriza
Keyword(s):  
Stellar Population ◽  
Spiral Galaxies ◽  
Broad Band ◽  
Nearby Galaxy ◽  
Ellipse Fitting ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Individual Star ◽  
The Individual

The first results of a study of the circumnuclear star-forming regions in HST broad band images of the nearby galaxy NGC4314 are presented. After modeling the bulge stellar population using ellipse fitting and subtracting the resulting model from the original images, aperture photometry of the individual star-forming regions in the ring was performed. For a total of 75 regions detected 3σ above the background, we obtained mean colors (f439—f569) = −0.72 ± 0.27, and (f569—f814) = −0.69 ± 0.35, with the NW regions being ∼ 0.5 mag bluer in both colors than the NE ones, an effect that may be caused by internal reddening.

Selection of one-dimensional sedimentation: models for on-line use

1995 ◽  
Vol 31 (2) ◽  
pp. 193-204 ◽  
Author(s):  
Koen Grijspeerdt ◽  
Peter Vanrolleghem ◽  
Willy Verstraete
Keyword(s):  
Steady State ◽  
Selection Criteria ◽  
Data Sets ◽  
Concentration Profiles ◽  
A Posteriori ◽  
One Dimensional ◽  
On Line ◽  
Dynamic Concentration ◽  
Selection Of ◽  
Modelling Task

A comparative study of several recently proposed one-dimensional sedimentation models has been made. This has been achieved by fitting these models to steady-state and dynamic concentration profiles obtained in a down-scaled secondary decanter. The models were evaluated with several a posteriori model selection criteria. Since the purpose of the modelling task is to do on-line simulations, the calculation time was used as one of the selection criteria. Finally, the practical identifiability of the models for the available data sets was also investigated. It could be concluded that the model of Takács et al. (1991) gave the most reliable results.

scholarly journals Searching for Mg ii absorbers in and around galaxy clusters

2021 ◽  
Vol 503 (3) ◽  
pp. 4309-4319
Author(s):  
Jong Chul Lee ◽  
Ho Seong Hwang ◽  
Hyunmi Song
Keyword(s):  
Galaxy Clusters ◽  
Detection Rate ◽  
Massive Star ◽  
Sloan Digital Sky Survey ◽  
Number Density ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Quasar Spectra ◽  
Sky Survey ◽  
The Galaxy

ABSTRACT To study environmental effects on the circumgalactic medium (CGM), we use the samples of redMaPPer galaxy clusters, background quasars, and cluster galaxies from the Sloan Digital Sky Survey (SDSS). With ∼82 000 quasar spectra, we detect 197 Mg ii absorbers in and around the clusters. The detection rate per quasar is 2.7 ± 0.7 times higher inside the clusters than outside the clusters, indicating that Mg ii absorbers are relatively abundant in clusters. However, when considering the galaxy number density, the absorber-to-galaxy ratio is rather low inside the clusters. If we assume that Mg ii absorbers are mainly contributed by the CGM of massive star-forming galaxies, a typical halo size of cluster galaxies is smaller than that of field galaxies by 30 ± 10 per cent. This finding supports that galaxy haloes can be truncated by interaction with the host cluster.

Individual effects in variation analysis: Model, software, and research design

2013 ◽  
Vol 25 (1) ◽  
pp. 89-118 ◽  
Author(s):  
John C. Paolillo
Keyword(s):  
Research Design ◽  
Fixed Effects ◽  
Selection Criteria ◽  
Current Approach ◽  
Variation Analysis ◽  
Analysis Model ◽  
Individual Level ◽  
Mixed Effects Modeling ◽  
Variationist Sociolinguistics ◽  
Selection Of

AbstractIndividual-level variation is a recurrent issue in variationist sociolinguistics. One current approach recommends addressing this via mixed-effects modeling. This paper shows that a closely related model with fixed effects for individual speakers can be directly estimated using Goldvarb. The consequences of employing different approaches to speaker variation are explored by using different model selection criteria. We conclude by discussing the relation of the statistical model to the assumptions of the research design, pointing out that nonrandom selection of speakers potentially violates the assumptions of models with random effects for speaker, and suggesting that a model with fixed effects for speakers may be a better alternative in these cases.

scholarly journals Using stellar population studies to determine the progenitors of GRBs and SNe

2009 ◽  
Vol 5 (S262) ◽  
pp. 436-437
Author(s):  
Christina C. Thöne ◽  
Lise Christensen ◽  
Johan P. U. Fynbo
Keyword(s):  
Emission Line ◽  
Stellar Population ◽  
Population Studies ◽  
Population Models ◽  
Host Galaxy ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions

AbstractWe present spatially resolved emission line studies of three nearby GRB and SN hosts with longslit and/or IFU observations. We compare the environment of the GRBs/SNe with those of other star-forming regions in the host galaxy and try to get informations on the progenitor from stellar population models and metallicities.

scholarly journals Clumpy Galaxies in the Early Universe

2006 ◽  
Vol 2 (S235) ◽  
pp. 376-380 ◽  
Author(s):  
Debra Meloy Elmegreen
Keyword(s):  
Star Formation ◽  
Early Universe ◽  
Spiral Galaxies ◽  
Star Forming ◽  
Wide Range ◽  
Thick Disks ◽  
Hubble Ultra Deep Field

AbstractClumpy galaxies are prominent in the early Universe. We present morphological and photometric properties of a wide range of galaxy types and their star-forming clumps in the Hubble Ultra Deep Field. Sizes, scale lengths, and scale heights suggest that galaxies grow by a factor of 2 fromz= 4 to the present, and that thick disks are present in the early Universe. The largest clumps of star formation are 107–109M⊙in different galaxies, much more massive than large star-forming complexes in local galaxies. Dissolved clumps may account for both the exponential disks and the early thick disks of spirals and proto-spiral galaxies.

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