Exploring chemical homogeneity in dwarf galaxies: a VLT-MUSE study of JKB 18

ABSTRACT Deciphering the distribution of metals throughout galaxies is fundamental in our understanding of galaxy evolution. Nearby, low-metallicity, star-forming dwarf galaxies, in particular, can offer detailed insight into the metal-dependent processes that may have occurred within galaxies in the early Universe. Here, we present VLT/MUSE observations of one such system, JKB 18, a blue diffuse dwarf galaxy with a metallicity of only 12 + log(O/H)=7.6 ± 0.2 (∼0.08 Z⊙). Using high spatial resolution integral-field spectroscopy of the entire system, we calculate chemical abundances for individual H ii regions using the direct method and derive oxygen abundance maps using strong-line metallicity diagnostics. With large-scale dispersions in O/H, N/H, and N/O of ∼0.5–0.6 dex and regions harbouring chemical abundances outside this 1σ distribution, we deem JKB 18 to be chemically inhomogeneous. We explore this finding in the context of other chemically inhomogeneous dwarf galaxies and conclude that neither the accretion of metal-poor gas, short mixing time-scales or self-enrichment from Wolf–Rayet stars are accountable. Using a galaxy-scale, multiphase, hydrodynamical simulation of a low-mass dwarf galaxy, we find that chemical inhomogeneities of this level may be attributable to the removal of gas via supernovae and the specific timing of the observations with respect to star formation activity. This study not only draws attention to the fact that dwarf galaxies can be chemically inhomogeneous, but also that the methods used in the assessment of this characteristic can be subject to bias.

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Influence of the Void Environment on Chemical Abundances in Dwarf Galaxies and Implications for Connecting Star Formation and Halo Mass

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006816 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 369-372

Author(s):

Kelly A. Douglass ◽

Michael S. Vogeley ◽

Renyue Cen

Keyword(s):

Dark Matter ◽

Star Formation ◽

Large Scale ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Direct Method ◽

Dark Matter Halo ◽

Chemical Abundances ◽

Abundance Estimates ◽

Galaxy Populations

AbstractWe study how the void environment affects the chemical evolution of galaxies by comparing the metallicity of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate oxygen and nitrogen abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. A substitute for the [OII] λ3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the direct method. We find that void dwarf galaxies have about the same oxygen abundances and slightly lower N/O ratios than dwarf galaxies in denser environments. The lower N/O ratios seen in void dwarf galaxies may indicate both delayed star formation and a dependence of cosmic downsizing on the large-scale environment. Similar oxygen abundances in the two dwarf galaxy populations might be evidence of larger ratios of dark matter halo mass to stellar mass in voids.

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Bar effect on gas-phase abundance gradients. I. Data sample and chemical abundances

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2246 ◽

2020 ◽

Vol 500 (2) ◽

pp. 2359-2379 ◽

Cited By ~ 1

Author(s):

A Zurita ◽

E Florido ◽

F Bresolin ◽

E Pérez-Montero ◽

I Pérez

Keyword(s):

Emission Line ◽

Gas Phase ◽

Direct Method ◽

Structural Parameters ◽

Companion Paper ◽

Strong Line ◽

H Ii Regions ◽

Chemical Abundances ◽

The Galaxy ◽

H Ii Region

ABSTRACT Studies of gas-phase radial metallicity profiles in spirals published in the last decade have diminished the importance of galactic bars as agents that mix and flatten the profiles, contradicting results obtained in the 1990s. We have collected a large sample of 2831 published H ii region emission-line fluxes in 51 nearby galaxies, including objects both with and without the presence of a bar, with the aim of revisiting the issue of whether bars affect the radial metal distribution in spirals. In this first paper of a series of two, we present the galaxy and the H ii region samples. The methodology is homogeneous for the whole data sample and includes the derivation of H ii region chemical abundances, structural parameters of bars and discs, galactocentric distances, and radial abundance profiles. We have obtained O/H and N/O abundance ratios from the Te-based (direct) method for a subsample of 610 regions, and from a variety of strong-line methods for the whole H ii region sample. The strong-line methods have been evaluated in relation to the Te-based one from both a comparison of the derived O/H and N/O abundances for individual H ii regions and a comparison of the abundance gradients derived from both methodologies. The median value and the standard deviation of the gradient distributions depend on the abundance method, and those based on the O3N2 indicator tend to flatten the steepest profiles, reducing the range of observed gradients. A detailed analysis and discussion of the derived O/H and N/O radial abundance gradients and y-intercepts for barred and unbarred galaxies is presented in the companion Paper II. The whole H ii region catalogue including emission-line fluxes, positions, and derived abundances is made publicly available on the CDS VizieR facility, together with the radial abundance gradients for all galaxies.

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Evolution of dwarf galaxy observable parameters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa298 ◽

2020 ◽

Vol 493 (1) ◽

pp. 638-650

Author(s):

Eimantas Ledinauskas ◽

Kastytis Zubovas

Keyword(s):

Galaxy Evolution ◽

Dwarf Galaxies ◽

Background Radiation ◽

Dwarf Galaxy ◽

High Redshift ◽

Stellar Mass ◽

Local Universe ◽

Isolated Galaxies ◽

Mass Assembly ◽

Hubble Time

ABSTRACT We present a semi-analytic model of isolated dwarf galaxy evolution and use it to study the build-up of observed correlations between dwarf galaxy properties. We analyse the evolution using models with averaged and individual halo mass assembly histories in order to determine the importance of stochasticity on the present-day properties of dwarf galaxies. The model has a few free parameters, but when these are calibrated using the halo mass–stellar mass and stellar mass–metallicity relations, the results agree with other observed dwarf galaxy properties remarkably well. Redshift evolution shows that even isolated galaxies change significantly over the Hubble time and that ‘fossil dwarf galaxies’ with properties equivalent to those of high-redshift analogues should be extremely rare, or non-existent, in the local Universe. A break in most galaxy property correlations develops over time, at a stellar mass $M_* \simeq 10^7 \, {\rm M_{\odot }}$. It is caused predominantly by the ionizing background radiation and can therefore in principle be used to constrain the properties of reionization.

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The Te[N ii]–Te[O iii] temperature relation in H ii regions and the reliability of strong-line methods

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1759 ◽

2020 ◽

Vol 497 (1) ◽

pp. 672-686

Author(s):

K Z Arellano-Córdova ◽

M Rodríguez

Keyword(s):

High Resolution ◽

Direct Method ◽

Strong Line ◽

Temperature Sensitive ◽

H Ii Regions ◽

Temperature Relation ◽

Degree Of Ionization ◽

Sensitive Line ◽

The One

ABSTRACT We use a sample of 154 observations of 124 H ii regions that have measurements of both Te[O iii] and Te[N ii], compiled from the literature, to explore the behaviour of the Te[O iii]–Te[N ii] temperature relation. We confirm that the relation depends on the degree of ionization and present a new set of relations for two different ranges of this parameter. We study the effects introduced by our temperature relations and four other available relations in the calculation of oxygen and nitrogen abundances. We find that our relations improve slightly on the results obtained with the previous ones. We also use a sample of 26 deep, high-resolution spectra to estimate the contribution of blending to the intensity of the temperature-sensitive line [O iii] λ4363, and we derive a relation to correct Te[O iii] for this effect. With our sample of 154 spectra, we analyse the reliability of the R, S, O3N2, N2, ONS, and C strong-line methods by comparing the metallicity obtained with these methods with the one implied by the direct method. We find that the strong-line methods introduce differences that reach ∼0.2 dex or more, and that these differences depend on O/H, N/O, and the degree of ionization.

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The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732241 ◽

2018 ◽

Vol 620 ◽

pp. A133 ◽

Cited By ~ 1

Author(s):

T. Richtler ◽

M. Hilker ◽

K. Voggel ◽

T. H. Puzia ◽

R. Salinas ◽

...

Keyword(s):

Galaxy Evolution ◽

Dwarf Galaxy ◽

Broad Band ◽

Hii Regions ◽

Diagnostic Tools ◽

Strong Line ◽

Main Body ◽

Surprising Result ◽

Star Forming ◽

The Galaxy

Context. The isolated elliptical (IE) NGC 7796 is accompanied by an interesting early-type dwarf galaxy, named NGC 7796-DW1. It exhibits a tidal tail, very boxy isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the bulk population of the galaxy, indicating a younger age. These properties are suggestive of a dwarf–dwarf merger remnant. Aims. Dwarf–dwarf mergers are poorly understood, but may have a high importance for dwarf galaxy evolution. We want to investigate the properties of the dwarf galaxy and its components to find more evidence for a dwarf–dwarf merger or for alternative formation scenarios. Methods. We use the Multi-Unit Spectroscopic Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract characteristic spectra to which we apply the STARLIGHT population synthesis software to obtain ages and metallicities of the various population components of the galaxy. This permits us to isolate the emission lines for which fluxes and flux ratios can be measured and to which strong-line diagnostic tools can be applied. Results. The galaxy’s main body is old and metal-poor. A surprising result is the extended line emission in the galaxy, forming a ring-like structure with a projected diameter of 2.2 kpc. The line ratios fall into the regime of HII-regions, although OB-stellar populations cannot be identified by spectral signatures. The low Hα surface brightnesses indicate unresolved star-forming substructures, which means that broad-band colours are not reliable age or metallicity indicators. Nucleus A is a relatively old (7 Gyr or older) and metalpoor super star cluster, most probably the nucleus of the dwarf, now displaced. The star-forming regions B and C show younger and distinctly more metal-rich components. The emission line ratios of regions B and C indicate an almost solar oxygen abundance, if compared with radiation models of HII regions. Oxygen abundances from empirical calibrations point to only half-solar. The ring-like Hα-structure does not exhibit signs of rotation or orbital movements. Conclusions. NGC 7796-DW1 occupies a particular role in the group of transition-type galaxies with respect to its origin and current evolutionary state, being the companion of an IE. The dwarf–dwarf merger scenario is excluded because of the missing metal-rich merger component. A viable alternative is gas accretion from a reservoir of cold, metal-rich gas. NGC 7796 has to provide this gas within its X-ray bright halo. As illustrated by NGC 7796-DW1, cold accretion may be a general solution to the problem of extended star formation histories in transition dwarf galaxies.

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Are Wolf-Rayet Stars Able to Pollute the Interstellar Medium of Galaxies? Results from Integral Field Spectroscopy

Advances in Astronomy ◽

10.1155/2013/837392 ◽

2013 ◽

Vol 2013 ◽

pp. 1-15 ◽

Cited By ~ 7

Author(s):

Enrique Pérez-Montero ◽

Carolina Kehrig ◽

Jarle Brinchmann ◽

José M. Vílchez ◽

Daniel Kunth ◽

...

Keyword(s):

Direct Method ◽

Spatial Scales ◽

Strong Line ◽

Chemical Abundances ◽

Local Pollution ◽

Integral Field Spectroscopy ◽

Field Spectroscopy ◽

Low Surface Brightness ◽

Low Metallicity ◽

Integral Field

We investigate the spatial distribution of chemical abundances in a sample of low metallicity Wolf-Rayet (WR) galaxies selected from the SDSS. We used the integral field spectroscopy technique in the optical spectral range (3700 Å–6850 Å) with PMAS attached to the CAHA 3.5 m telescope. Our statistical analysis of the spatial distributions of O/H and N/O, as derived using the direct method or strong-line parameters consistent with it, indicates that metallicity is homogeneous in five out of the six analysed objects in scales of the order of several kpc. Only in the object WR404 is a gradient of metallicity found in the direction of the low surface brightness tail. In contrast, we found an overabundance of N/O in spatial scales of the order of hundreds of pc associated with or close to the positions of the WR stars in 4 out of the 6 galaxies. We exclude possible hydrodynamical causes, such as the metal-poor gas inflow, for this local pollution by means of the analysis of the mass-metallicity relation (MZR) and mass-nitrogen-to-oxygen relation (MNOR) for the WR galaxies catalogued in the SDSS.

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Unravelling the enigmatic ISM conditions in Minkowski’s object

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3121 ◽

2020 ◽

Vol 499 (4) ◽

pp. 4940-4960

Author(s):

Henry R M Zovaro ◽

Robert Sharp ◽

Nicole P H Nesvadba ◽

Lisa Kewley ◽

Ralph Sutherland ◽

...

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Dwarf Galaxy ◽

Formation Rate ◽

Theoretical Models ◽

Strong Line ◽

Valuable Insight ◽

Jet Interaction ◽

Star Forming ◽

The Galaxy

ABSTRACT Local examples of jet-induced star formation lend valuable insight into its significance in galaxy evolution and can provide important observational constraints for theoretical models of positive feedback. Using optical integral field spectroscopy, we present an analysis of the ISM conditions in Minkowski’s object (z = 0.0189), a peculiar star-forming dwarf galaxy located in the path of a radio jet from the galaxy NGC 541. Full spectral fitting with ppxf indicates that Minkowski’s object primarily consists of a young stellar population $\sim \! 10\, \rm Myr$ old, confirming that the bulk of the object’s stellar mass formed during a recent jet interaction. Minkowski’s object exhibits line ratios largely consistent with star formation, although there is evidence for a low level ($\lesssim \! 15 \, \rm per \, cent$) of contamination from a non-stellar ionizing source. Strong-line diagnostics reveal a significant variation in the gas-phase metallicity within the object, with $\log \left(\rm O / H \right) + 12$ varying by $\sim \! 0.5\, \rm dex$, which cannot be explained by in-situ star formation, an enriched outflow from the jet, or enrichment of gas in the stellar bridge between NGC 541 and NGC 545/547. We hypothesize that Minkowski’s object either (i) was formed as a result of jet-induced star formation in pre-existing gas clumps in the stellar bridge, or (ii) is a gas-rich dwarf galaxy that is experiencing an elevation in its star formation rate due to a jet interaction, and will eventually redden and fade, becoming an ultradiffuse galaxy as it is processed by the cluster.

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Low Luminosity Galaxies

Publications of the Astronomical Society of Australia ◽

10.1071/as04046 ◽

2004 ◽

Vol 21 (4) ◽

pp. 360-365 ◽

Cited By ~ 4

Author(s):

J. I. Davies ◽

S. Sabatini ◽

S. Roberts

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Large Scale ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Building Blocks ◽

Large Mass ◽

Dark Matter Halos ◽

Cluster Environment ◽

Dense Cluster

AbstractLow luminosity (dwarf) galaxies play a crucial role in our current theories of galaxy and large scale structure formation. In the hierarchical picture they are the building blocks from which other structures form. These theories in their basic form overpredict the numbers of small dark matter halos (dwarf galaxies?) unless some form of star formation supression is invoked. In this paper we describe observations of dwarf galaxies in a range of different environments. We find that there are far too few dwarf galaxies in low density environments to be compatible with the theories. These observations are not consistent with an environment-independent mechanism suppressing dwarf galaxy formation. It is also not clear how these mechanisms can supress star formation if dwarf galaxies have large mass-to-light ratios (≈100). Either the whole idea of hierarchical galaxy formation has to be rejected or other environmentally dependent physical processes have to be invoked. We suggest that small, gas-rich dI galaxies have their evolution rapidly advanced as they move into the dense cluster environment.

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The orientation of planes of dwarf galaxies in the quasi-linear Universe

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2852 ◽

2019 ◽

Vol 490 (3) ◽

pp. 3786-3792 ◽

Cited By ~ 4

Author(s):

Noam I Libeskind ◽

Edoardo Carlesi ◽

Oliver Müller ◽

Marcel S Pawlowski ◽

Yehuda Hoffman ◽

...

Keyword(s):

Velocity Field ◽

Large Scale ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Large Scale Structure ◽

Formation Mechanisms ◽

Linear Regime ◽

Local Universe ◽

Shear Tensor ◽

Linear Field

ABSTRACT To date at least 10 highly flattened planes of dwarf galaxies are claimed to have been discovered in the Local Universe. The origin of these planes of galaxies remains unknown. One suggestion is that they are related to the large-scale structure of the cosmic web. A recent study found that the normal of a number of these dwarf galaxy planes is very closely aligned with the eigenvector of the shear tensor corresponding to the direction of greatest collapse obtained by reconstructing the full velocity field in the linear regime. Here we extend that work by both considering an additional 5 planes beyond the five examined previously and examining the alignment with respect to the quasi-linear field, a more sophisticated reconstruction, which is a better approximation on smaller (quasi-linear) scales. Our analysis recovers the previous result while not finding a significantly tight alignment with the additional five planes. However, the additional five plane normals also do not appear to be randomly oriented. We conclude that this could be due either to the normals of the new planes being poorly defined and described; the quasi-linear field at those locations being poorly constrained; or different formation mechanisms for the orientation of planes of dwarf galaxies.

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Dwarf galaxies at low and high redshift

Proceedings of the International Astronomical Union ◽

10.1017/s174392131800652x ◽

2018 ◽

Vol 14 (S344) ◽

pp. 437-445

Author(s):

Xu Kong ◽

Jianhui Lian ◽

Yulong Gao ◽

Zuyi Chen ◽

Guangwen Chen ◽

...

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Near Infrared ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

High Redshift ◽

Formation Rate ◽

Mass Star ◽

Chemical Enrichment ◽

Galaxy Sample

AbstractThe overwhelming majority of galaxies in the Universe are dwarf galaxies. But although they are important components in understanding galaxy evolution, these systems are typically too faint to be observed at high redshifts. However, we are able to obtain an unobscured view of early star formation and chemical enrichment in these galaxies at low redshift and low-redshift analogs at high redshift. In this talk, I will review the mass-metallicity relation, the mass-star formation rate relation of galaxies, the classifications of dwarf galaxies, and the importance of dwarf galaxies for both astronomy and physics. Then I will introduce some work in our group on connections among between different types of dwarf galaxies,the mass-metallicity relations and the main sequence relations of dwarf galaxies, using the deep optical and near infrared images and spectra of large dwarf galaxy sample. At the end, I will talk about some projects of dwarf galaxies we are working on, including the spectroscopic survey for compact dwarf galaxies using the LAMOST.

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