scholarly journals The VIRUS-P Exploration of Nearby Galaxies (VENGA): the stellar populations and assembly of NGC 2903’s bulge, bar, and outer disc

2020 ◽  
Vol 493 (3) ◽  
pp. 4094-4106 ◽  
Author(s):  
Andreia Carrillo ◽  
Shardha Jogee ◽  
Niv Drory ◽  
Kyle F Kaplan ◽  
Guillermo Blanc ◽  
...  
Keyword(s):  
Stellar Populations ◽  
Population Synthesis ◽  
Sky Survey ◽  
Stellar Population Synthesis ◽  
Merger Event ◽  
Major Merger ◽  
Nearby Galaxies ◽  
Minor Mergers ◽  
High Metallicity ◽  
Band Image

ABSTRACT We study the stellar populations and assembly of the nearby spiral galaxy NGC 2903’s bulge, bar, and outer disc using the VIRUS-P Exploration of Nearby Galaxies IFS survey. We observe NGC 2903 with a spatial resolution of 185 pc using the Mitchell Spectrograph’s 4.25 arcsec fibres at the 2.7 Harlan J. Smith telescope. Bulge–bar–disc decomposition on the Two Micron All-Sky Survey (2MASS) Ks-band image of NGC 2903 shows that it has ∼6 per cent, 6 per cent, and 88 per cent, of its stellar mass in the bulge, bar, and outer disc, respectively, and its bulge has a low Sérsic index of ∼0.27, suggestive of a discy bulge. We perform stellar population synthesis and find that the outer disc has 46 per cent of its mass in stars >5 Gyr, 48 per cent in stars between 1 and 5 Gyr, and <10 per cent in younger stars. Its stellar bar has 65 per cent of its mass in ages 1–5 Gyr and has metallicities similar to the outer disc, suggestive of the evolutionary picture where the bar forms from disc material. Its bulge is mainly composed of old high-metallicity stars though it also has a small fraction of young stars. We find enhanced metallicity in the spiral arms and central region, tracing areas of high star formation as seen in the Hα map. These results are consistent with the idea that galaxies of low bulge-to-total mass ratio and low bulge Sérsic index like NGC 2903 has not had a recent major merger event, but has instead grown mostly through minor mergers and secular processes.

scholarly journals Imaging of NGC 5907's stellar stream

2015 ◽  
Vol 11 (S317) ◽  
pp. 324-325
Author(s):  
Seppo Laine ◽  
Carl J. Grillmair ◽  
David Martínez–Delgado ◽  
Aaron J. Romanowsky ◽  
Peter L. Capak ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Stellar Population ◽  
Population Synthesis ◽  
Stellar Population Synthesis ◽  
Major Merger ◽  
High Metallicity

AbstractWe have obtained deep g, r, and i-band Subaru and ultra-deep 3.6 μm IRAC images of parts of the multiply-wrapped stellar stream around the nearby edge-on galaxy NGC 5907. We have fitted the surface brightness measurements of the stream with FSPS stellar population synthesis models to derive the metallicity and age of the brightest parts of the stream. The resulting relatively high metallicity ([Fe/H] = −0.3) is consistent with a major merger scenario but a satellite accretion event cannot be ruled out.

scholarly journals Ultraviolet spectra of extreme nearby star-forming regions: Evidence for an overabundance of very massive stars

2021 ◽  
Vol 503 (4) ◽  
pp. 6112-6135
Author(s):  
Peter Senchyna ◽  
Daniel P Stark ◽  
Stéphane Charlot ◽  
Jacopo Chevallard ◽  
Gustavo Bruzual ◽  
...  
Keyword(s):  
Stellar Wind ◽  
Massive Stars ◽  
Stellar Populations ◽  
Population Synthesis ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
High Incidence ◽  
Stellar Population Synthesis ◽  
Stellar Masses

ABSTRACT As deep spectroscopic campaigns extend to higher redshifts and lower stellar masses, the interpretation of galaxy spectra depends increasingly upon models for very young stellar populations. Here we present new HST/COS ultraviolet spectroscopy of seven nearby (<120 Mpc) star-forming regions hosting very young stellar populations (∼4–20 Myr) with optical Wolf–Rayet stellar wind signatures, ideal laboratories in which to benchmark these stellar models. We detect nebular C iii] in all seven, but at equivalent widths uniformly <10 Å. This suggests that even for very young stellar populations, the highest equivalent width C iii] emission at ≥15 Å is reserved for inefficiently cooled gas at metallicities at or below that of the SMC. The spectra also reveal strong C iv P-Cygni profiles and broad He ii emission formed in the winds of massive stars, including some of the most prominent He ii stellar wind lines ever detected in integrated spectra. We find that the latest stellar population synthesis prescriptions with improved treatment of massive stars nearly reproduce the entire range of stellar He ii wind strengths observed here. However, we find that these models cannot simultaneously match the strongest wind features alongside the optical nebular line constraints. This discrepancy can be naturally explained by an overabundance of very massive stars produced by a high incidence of binary mass transfer and mergers occurring on short ≲10 Myr time-scales, suggesting these processes may be crucial for understanding systems dominated by young stars both nearby and in the early Universe.

scholarly journals Stellar population synthesis: Application To Galactic Bulges

1993 ◽  
Vol 153 ◽  
pp. 133-150
Author(s):  
N. Arimoto
Keyword(s):  
Observational Data ◽  
Stellar Population ◽  
Stellar Populations ◽  
Population Synthesis ◽  
Firm Conclusion ◽  
Formation History ◽  
Stellar Population Synthesis ◽  
Central Regions ◽  
History Of ◽  
Metallicity Distribution

The stellar populations give traces of the formation history of the bulges. The metallicity distribution of K-giants in the Galactic bulge resembles to that of the giant ellipticals. There seems to be no conspicuous colour-magnitude relation intrinsic to the bulges. This can be explained if the bulges formed by the dissipative collapse of central regions of proto-galaxies followed by the supernova-driven bulge wind which was induced later than the dwarf ellipticals of the similar mass (the biased wind). Unfortunately, the observational data available at present of stellar populations of the bulges are not yet sufficient to get a firm conclusion on the origin of the bulges.

scholarly journals Applications of Stellar Population Synthesis in the Distant Universe

Galaxies ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 6 ◽  
Author(s):  
Elizabeth R. Stanway
Keyword(s):  
Physical Properties ◽  
Stellar Population ◽  
Stellar Populations ◽  
Population Synthesis ◽  
Signal To Noise ◽  
Distant Galaxies ◽  
Stellar Population Synthesis ◽  
Noise Data

Comparison with artificial galaxy models is essential for translating the incomplete and low signal-to-noise data we can obtain on astrophysical stellar populations to physical interpretations which describe their composition, physical properties, histories and internal conditions. In particular, this is true for distant galaxies, whose unresolved light embeds clues to their formations and evolutions, and their impacts on their wider environs. Stellar population synthesis models are now used as the foundation of analysis at all redshifts, but are not without their problems. Here we review the use of stellar population synthesis models, with a focus on applications in the distant Universe.

Optical properties of CSS/GPS sources

2019 ◽  
Vol 15 (S359) ◽  
pp. 357-359
Author(s):  
Raquel S. Nascimento ◽  
Alberto Rodríguez-Ardila ◽  
Marcos F. Faria ◽  
Murilo Marinello ◽  
Luis G. Dahmer-Hahn
Keyword(s):  
Optical Properties ◽  
Strong Correlation ◽  
Stellar Population ◽  
Stellar Populations ◽  
Optical Spectra ◽  
Radio Sources ◽  
Population Synthesis ◽  
Stellar Population Synthesis ◽  
The Impact

AbstractIn this work, we study the optical properties of 58 CSS/GPS radio sources selected from the literature in order to determine the impact of the radio-jet in the circumnuclear environment of these objects. We obtained optical spectra for all sources from SDSS-DR12 and performed a stellar population synthesis using the Starlight code. Our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources.

Stellar population synthesis of jellyfish galaxies

2019 ◽  
Vol 15 (S359) ◽  
pp. 255-256
Author(s):  
Gabriel M. Azevedo ◽  
Ana L. Chies Santos ◽  
Rogério Riffel ◽  
Augusto Lassen ◽  
Marina Trevisan ◽  
...  
Keyword(s):  
Stellar Population ◽  
Stellar Populations ◽  
Population Synthesis ◽  
Data Cubes ◽  
Ram Pressure ◽  
Stellar Population Synthesis

AbstractJellyfish are the most extreme cases of galaxies undergoing ram-pressure stripping. In order to analyse the stellar populations distribution along these galaxies, we have performed stellar population synthesis in data cubes of jellyfish from the GASP programme, using both Starlight and FADO codes.

scholarly journals Merger signatures in low excitation radio galaxies

2019 ◽  
Vol 489 (2) ◽  
pp. 2308-2312
Author(s):  
David Garofalo
Keyword(s):  
Time Scales ◽  
Radio Galaxies ◽  
Direct Result ◽  
Average Lifetime ◽  
Merger Event ◽  
Order Of Magnitude ◽  
Major Merger ◽  
Cluster Environment ◽  
Minor Mergers ◽  
Halo Gas

ABSTRACT While no consensus governs our understanding of the origin of low-redshift radio galaxies, the possibility that mergers may trigger accretion from hot cluster halo gas has spurred a recent search for such signatures. Evidence for mergers is at best tenuous, however, and even when found, generates more questions than answers. With scant evidence for minor mergers, some connection to major mergers is found in isolated environments but not where one would expect, i.e. in clusters. We provide an explanation for these recent results by Gordon et al. on the relevance of major mergers in low excitation radio galaxies (LERGs) at low redshift. While LERGs are not the direct result of a merger, we describe how they form in clusters in only a few million years while that time-scale is an order of magnitude longer in field environments. As a result of these different time-scales, the average lifetime of a cluster LERG is estimated at an order of magnitude greater value than for field LERGs. Observing an LERG in the cluster environment, therefore, will tend to occur when greater time has passed since the major merger event that produced its high excitation radio galaxy ancestor, such that fewer signatures of that event remain visible. We provide simple estimates for the fraction of LERGs as a function of environment that are directly related to these time-scales, obtaining a probability of about 7 per cent that field LERGs will show merger signatures and 3 per cent for clusters, showing that theory and observation match if major merger signatures remain visible for a few hundred million years.

scholarly journals Morphology-assisted galaxy mass-to-light predictions using deep learning

2019 ◽  
Vol 624 ◽  
pp. A102 ◽  
Author(s):  
Wouter Dobbels ◽  
Serge Krier ◽  
Stephan Pirson ◽  
Sébastien Viaene ◽  
Gert De Geyter ◽  
...  
Keyword(s):  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Stellar Mass ◽  
Gradient Boosting ◽  
Spectral Energy ◽  
Population Synthesis ◽  
Gradient Boosting Machine ◽  
Stellar Population Synthesis ◽  
Additional Constraints ◽  
Band Image

Context. One of the most important properties of a galaxy is the total stellar mass, or equivalently the stellar mass-to-light ratio (M/L). It is not directly observable, but can be estimated from stellar population synthesis. Currently, a galaxy’s M/L is typically estimated from global fluxes. For example, a single global g − i colour correlates well with the stellar M/L. Spectral energy distribution (SED) fitting can make use of all available fluxes and their errors to make a Bayesian estimate of the M/L. Aims. We want to investigate the possibility of using morphology information to assist predictions of M/L. Our first goal is to develop and train a method that only requires a g-band image and redshift as input. This will allows us to study the correlation between M/L and morphology. Next, we can also include the i-band flux, and determine if morphology provides additional constraints compared to a method that only uses g- and i-band fluxes. Methods. We used a machine learning pipeline that can be split in two steps. First, we detected morphology features with a convolutional neural network. These are then combined with redshift, pixel size and g-band luminosity features in a gradient boosting machine. Our training target was the M/L acquired from the GALEX-SDSS-WISE Legacy Catalog, which uses global SED fitting and contains galaxies with z ∼ 0.1. Results. Morphology is a useful attribute when no colour information is available, but can not outperform colour methods on its own. When we combine the morphology features with global g- and i-band luminosities, we find an improved estimate compared to a model which does not make use of morphology. Conclusions. While our method was trained to reproduce global SED fitted M/L, galaxy morphology gives us an important additional constraint when using one or two bands. Our framework can be extended to other problems to make use of morphological information.

scholarly journals Using Evolution Strategies to Perform Stellar Population Synthesis for Galaxy Spectra from SDSS

2012 ◽  
pp. 276-286
Author(s):  
Juan Carlos Gomez ◽  
Olac Fuentes
Keyword(s):  
Stellar Population ◽  
Theoretical Models ◽  
Parameter Extraction ◽  
Sloan Digital Sky Survey ◽  
Evolution Strategies ◽  
Physical Parameters ◽  
Population Synthesis ◽  
Sky Survey ◽  
Stellar Population Synthesis ◽  
Simple Difference

In this work, the authors employ Evolution Strategies (ES) to automatically extract a set of physical parameters, corresponding to stellar population synthesis, from a sample of galaxy spectra taken from the Sloan Digital Sky Survey (SDSS). This parameter extraction is presented as an optimization problem and being solved using ES. The idea is to reconstruct each galaxy spectrum by means of a linear combination of three different theoretical models for stellar population synthesis. This combination produces a model spectrum that is compared with the original spectrum using a simple difference function. The goal is to find a model that minimizes this difference, using ES as the algorithm to explore the parameter space. This paper presents experimental results using a set of 100 spectra from SDSS Data Release 2 that show that ES are very well suited to extract stellar population parameters from galaxy spectra. Additionally, in order to better understand the performance of ES in this problem, a comparison with two well known stochastic search algorithms, Genetic Algorithms (GA) and Simulated Annealing (SA), is presented.

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