Galaxies

Research

5358 KiB

Open AccessArticle

Characterization of Bars Induced by Interactions

by Inma Martinez-Valpuesta, José Alfonso López Aguerri and César González-García

Galaxies 2016, 4(2), 7; https://doi.org/10.3390/galaxies4020007 - 25 May 2016

Cited by 12 | Viewed by 3601

Whether the formation of bars is triggered by interactions or by internal processes has been discussed for many decades. In this work, we study differences between both mechanisms by means of numerical simulations. We relate our analysis to fly-by interactions in different mass [...] Read more.

Whether the formation of bars is triggered by interactions or by internal processes has been discussed for many decades. In this work, we study differences between both mechanisms by means of numerical simulations. We relate our analysis to fly-by interactions in different mass groups or clusters according to the velocity of the encounters. We find that once the bar is created, the interaction does not much affect its evolution. We also find that bars can be triggered purely by a slow interaction. Those bars affected or triggered by interaction stay for a longer time in the slow regime, i.e., the corotation radius is more than 1.4 times the bar radius. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

8187 KiB

Open AccessArticle

Fossil Systems; a Multi-wavelength Approach towards Understanding Galaxy Formation

by Habib G. Khosroshahi, Halime Miraghaei and Mojtaba Raouf

Galaxies 2016, 4(2), 5; https://doi.org/10.3390/galaxies4020005 - 25 Mar 2016

Cited by 1 | Viewed by 3823

Abstract

Fossil systems are understood to be the end product of galaxy mergers within groups and clusters. Their halo morphology points to their relaxed/virialised nature, thus allowing them to be employed as observational probes for the evolution of cosmic structures, their thermodynamics and dark [...] Read more.

Fossil systems are understood to be the end product of galaxy mergers within groups and clusters. Their halo morphology points to their relaxed/virialised nature, thus allowing them to be employed as observational probes for the evolution of cosmic structures, their thermodynamics and dark matter distribution. Cosmological simulations, and their underlying models, are broadly consistent with the early formation epoch for fossils. In a series of studies we have looked into galaxy properties and intergalactic medium (IGM) in fossils, across a wide range of wavelengths, from X-ray through optical to the radio, to have a better understanding of their nature, the attributed halo age, IGM heating and their AGNs and use them as laboratories to constrain galaxy formation models. Adhering to one of less attended properties of fossils, using the the Millennium Simulation, we combine luminosity gap with luminosity segregation (the brightest galaxy offset from the group luminosity centroid) to identify the most dynamically relaxed galaxy groups which allows us to reveal brand new observational connections between galaxies and their environments. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Graphical abstract

469 KiB

Open AccessArticle

Investigation of the Stellar Population of Several Polar Ring Galaxies

by Liliya Shalyapina, Gulnara Karataeva, Olga Merkulova, Valeriya Yakovleva and Nina Yablokova

Galaxies 2016, 4(1), 2; https://doi.org/10.3390/galaxies4010002 - 05 Jan 2016

Viewed by 3905

Abstract

We present results of our investigation of two multi-spin galaxies which were taken from the catalog of polar ring galaxies. All of them possess nucleus-like knots. An analysis of gas and stars kinematics and study of the stellar population were carried out for [...] Read more.

We present results of our investigation of two multi-spin galaxies which were taken from the catalog of polar ring galaxies. All of them possess nucleus-like knots. An analysis of gas and stars kinematics and study of the stellar population were carried out for these objects. A complex structure and peculiar kinematics of both components were revealed. The observed distribution of the stellar age and metallicity in central parts of galaxies (radius is about 8″) and along directions through their knots helps us to understand the merging processes and make conclusion of the knots’ nature in these objects. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

816 KiB

Open AccessArticle

Hidden Imprints of Minor Merging in Early-Type Galaxies: Inner Polar Rings and Inclined Large-Scale Gaseous Disks In S0s

by Olga Sil’chenko

Galaxies 2016, 4(1), 1; https://doi.org/10.3390/galaxies4010001 - 24 Dec 2015

Cited by 2 | Viewed by 3904

Abstract

I discuss my latest observational data and ideas about decoupled gaseous subsystems in nearby lenticular galaxies. As an extreme case of inclined gaseous disks, I demonstrate a sample of inner polar disks, derive their incidence, about 10% among the volume-limited nearby S0 galaxies, [...] Read more.

I discuss my latest observational data and ideas about decoupled gaseous subsystems in nearby lenticular galaxies. As an extreme case of inclined gaseous disks, I demonstrate a sample of inner polar disks, derive their incidence, about 10% among the volume-limited nearby S0 galaxies, and discuss their origin. However, large-scale decoupled gaseous disks at intermediate inclinations are also a rather common phenomenon among the field S0 galaxies. I suggest that the geometry of outer gas accretion and the final morphology of the galaxy may be tightly related: inclined gas infall may prevent star formation in the accreted disk and force the disk galaxy to be a lenticular. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

437 KiB

Open AccessArticle

Interactions, Starbursts, and Star Formation

by Johan H. Knapen and Miguel Querejeta

Galaxies 2015, 3(4), 220-226; https://doi.org/10.3390/galaxies3040220 - 18 Dec 2015

Cited by 2 | Viewed by 3623

Abstract

We study how interactions between galaxies affect star formation within them by considering a sample of almost 1500 of the nearest galaxies, all within a distance of ∼45 Mpc. We use the far-IR emission to define the massive star formation rate (SFR), and [...] Read more.

We study how interactions between galaxies affect star formation within them by considering a sample of almost 1500 of the nearest galaxies, all within a distance of ∼45 Mpc. We use the far-IR emission to define the massive star formation rate (SFR), and then normalise the SFR by the stellar mass of the galaxy to obtain the specific star formation rate (SSFR). We explore the distribution of (S)SFR with morphological type and with stellar mass. We calculate the relative enhancement of SFR and SSFR for each galaxy by normalising them by the median SFR and SSFR values of individual control samples of similar non-interacting galaxies. We find that both the median SFR and SSFR are enhanced in interacting galaxies, and more so as the degree of interaction is higher. The increase is moderate, reaching a maximum of a factor of 1.9 for the highest degree of interaction (mergers). While the SFR and SSFR are enhanced statistically by interactions, in many individual interacting galaxies they are not enhanced at all. Our study is based on a representative sample of nearby galaxies and should be used to place constraints on studies based on samples of galaxies at larger distances. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

1435 KiB

Open AccessArticle

The Ongoing Growth of the M87 Halo through Accretion Events

by Alessia Longobardi, Magda Arnaboldi and Ortwin Gerhard

Galaxies 2015, 3(4), 212-219; https://doi.org/10.3390/galaxies3040212 - 18 Dec 2015

Cited by 2 | Viewed by 3683

Abstract

Planetary nebulas (PNs) offer a unique tool to investigate the outer regions of massive galaxies because their strong [OIII]λ5007Å emission line makes them detectable out to several effective radii from the galaxy’s centre. We use a deep and extended spectroscopic survey [...] Read more.

Planetary nebulas (PNs) offer a unique tool to investigate the outer regions of massive galaxies because their strong [OIII]λ5007Å emission line makes them detectable out to several effective radii from the galaxy’s centre. We use a deep and extended spectroscopic survey of PNs (∼300 objects) to study the spatial distribution, the kinematics and the stellar populations in the extended outer halo of the bright elliptical galaxy M87 (NGC 4486) in the Virgo cluster. We show that in the Virgo core, M87 stellar halo and the intracluster light are two distinct dynamical components, with different velocity distributions. Moreover the synergy of the PN kinematical information and the deep V/B-band photometry revealed an ongoing accretion event in the outer regions of M87. This satellite accretion represents a non-negligible perturbation of the halo properties: beyond 60 kpc the M87 halo is still growing with 60% of its light being added by the accretion event at the distance where it is detected. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

3731 KiB

Open AccessArticle

Creating S0s with Major Mergers: A 3D View

by Miguel Querejeta, M. Carmen Eliche-Moral, Trinidad Tapia, Alejandro Borlaff, Glenn Van de Ven, Mariya Lyubenova, Marie Martig, Jesús Falcón-Barroso, Jairo Méndez-Abreu, Jaime Zamorano and Jesús Gallego

Galaxies 2015, 3(4), 202-211; https://doi.org/10.3390/galaxies3040202 - 03 Dec 2015

Cited by 2 | Viewed by 4083

Abstract

A number of simulators have argued that major mergers can sometimes preserve discs, but the possibility that they could explain the emergence of lenticular galaxies (S0s) has been generally neglected. In fact, observations of S0s reveal a strong structural coupling between their bulges [...] Read more.

A number of simulators have argued that major mergers can sometimes preserve discs, but the possibility that they could explain the emergence of lenticular galaxies (S0s) has been generally neglected. In fact, observations of S0s reveal a strong structural coupling between their bulges and discs, which seems difficult to reconcile with the idea that they come from major mergers. However, in our recent papers we have used N-body simulations of binary mergers to show that, under favourable conditions, discs are first destroyed but soon regrow out of the leftover debris, matching observational photometric scaling relations. Additionally, we have shown how the merger scenario agrees with the recent discovery that S0s and most spirals are not compatible in an angular momentum–concentration plane. This important result from CALIFA constitutes a serious objection to the idea that spirals transform into S0s mainly by fading (e.g., via ram-pressure stripping, as that would not explain the observed simultaneous change in λ Re and concentration), but our simulations of major mergers do explain that mismatch. From such a 3D comparison we conclude that mergers must be a relevant process in the build-up of the current population of S0s. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Graphical abstract

909 KiB

Open AccessArticle

Back to the Green Valley: How to Rejuvenate an S0 Galaxy through Minor Mergers

by Michela Mapelli

Galaxies 2015, 3(4), 192-201; https://doi.org/10.3390/galaxies3040192 - 13 Nov 2015

Cited by 4 | Viewed by 5358

Abstract

About half of the S0 galaxies in the nearby Universe show signatures of recent or ongoing star formation. Whether these S0 galaxies were rejuvenated by the accretion of fresh gas is still controversial. We study minor mergers of a gas-rich dwarf galaxy with [...] Read more.

About half of the S0 galaxies in the nearby Universe show signatures of recent or ongoing star formation. Whether these S0 galaxies were rejuvenated by the accretion of fresh gas is still controversial. We study minor mergers of a gas-rich dwarf galaxy with an S0 galaxy, by means of N-body smoothed-particle hydrodynamics simulations. We find that minor mergers trigger episodes of star formation in the S0 galaxy, lasting for \(\sim\)10 Gyr. One of the most important fingerprints of the merger is the formation of a gas ring in the S0 galaxy. The ring is reminiscent of the orbit of the satellite galaxy, and its lifetime depends on the merger properties: polar and counter-rotating satellite galaxies induce the formation of long-lived smooth gas rings. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Graphical abstract

804 KiB

Open AccessArticle

Tidal Dwarf Galaxies: Disc Formation at \(z\simeq0\)

by Federico Lelli, Pierre-Alain Duc, Elias Brinks and Stacy S. McGaugh

Galaxies 2015, 3(4), 184-191; https://doi.org/10.3390/galaxies3040184 - 05 Nov 2015

Cited by 5 | Viewed by 4639

Abstract

Collisional debris around interacting and post-interacting galaxies often display condensations of gas and young stars that can potentially form gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent results on TDGs, which are originally published in Lelli et al. (2015, A&A).We study [...] Read more.

Collisional debris around interacting and post-interacting galaxies often display condensations of gas and young stars that can potentially form gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent results on TDGs, which are originally published in Lelli et al. (2015, A&A).We study a sample of six TDGs around three different interacting systems, using high-resolution HI observations from the Very Large Array. We find that the HI emission associated to TDGs can be described by rotating disc models. These discs, however, would have undergone less than one orbit since the time of the TDG formation, raising the question of whether they are in dynamical equilibrium. Assuming that TDGs are in dynamical equilibrium, we find that the ratio of dynamical mass to baryonic mass is consistent with one, implying that TDGs are devoid of dark matter. This is in line with the results of numerical simulations where tidal forces effectively segregate dark matter in the halo from baryonic matter in the disc, which ends up forming tidal tails and TDGs. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Graphical abstract

535 KiB

Open AccessArticle

The CALIFA Survey: Exploring the Oxygen Abundance in the Local Universe

by Sebastian F. Sánchez, Laura Sánchez-Menguiano, Raffaella Marino, F. Fabian Rosales-Ortega, Isabel Pérez, Armando Gil De Paz, Enrique Pérez, C. Jakob Walcher and Carlos López-Cobá

Galaxies 2015, 3(4), 164-183; https://doi.org/10.3390/galaxies3040164 - 05 Nov 2015

Cited by 5 | Viewed by 5034

Abstract

We present here a review of the latest results on the spatially-resolved analysis of the stellar populations and ionized gas of disk-dominated galaxies based on Calar Alto Legacy Integral Field Area (CALIFA) data. CALIFA is an ongoing integral field spectroscopy (IFS) survey of [...] Read more.

We present here a review of the latest results on the spatially-resolved analysis of the stellar populations and ionized gas of disk-dominated galaxies based on Calar Alto Legacy Integral Field Area (CALIFA) data. CALIFA is an ongoing integral field spectroscopy (IFS) survey of galaxies in the Local Universe (0.005 < z < 0.03) that has already obtained spectroscopic information up to \(\sim\)2.5 \(r_e\) with a spatial resolution better than \(\sim\)1 kpc for a total number of more than 600 galaxies of different morphological types, covering the color-magnitude diagram up to M\(_{\rm R}<-\)18 mag. With nearly 2000 spectra obtained for each galaxy, CALIFA offers one of the best IFU datasets to study the star formation histories and chemical enrichment of galaxies. In this article, we focus on the main results from the analysis of the oxygen abundances based on the study of ionized gas in H II regions and individual spaxels and their relation to the global properties of galaxies, using an updated/revised dataset with more galaxies and ionized regions. In summary, we have confirmed previous published results indicating that: (1) the M-Z relation does not present a secondary relation to the star formation rate, when the abundance is measured at the effective radius; (2) the oxygen abundance presents a strong correlation with the stellar surface density (∑-Z relation); (3) the oxygen abundance profiles present three well-defined regimes: (i) an overall negative radial gradient between 0.5 and 2 \(r_e\), with a characteristic slope of \(\alpha_{O/H}\) \(\sim\)\(-\)0.1 dex/\(r_e\); (ii) a universal flattening beyond \(>\)2 \(r_e\); and (iii) an inner drop at \(<\)0.5 \(r_e\) that depends on mass; (4) the presence of bending in the surface brightness profile of disk galaxies is not clearly related to either the change in the shape of the oxygen abundance profile or the properties of the underlying stellar population. All of these results indicate that disk galaxies present an overall inside-out growth, with chemical enrichment and stellar mass growth tightly correlated and dominated by local processes and limited effects of radial mixing or global outflows. However, clear deviations are shown with respect to this simple scenario, which affect the abundance profiles in both the innermost and outermost regions of galaxies. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

695 KiB

Open AccessCommunication

Isolated Galaxies versus Interacting Pairs with MaNGA

by María Del Carmen Argudo Fernández, Fangting Yuan, Shiyin Shen, Jun Yin, Ruixiang Chang and Shuai Feng

Galaxies 2015, 3(4), 156-163; https://doi.org/10.3390/galaxies3040156 - 30 Oct 2015

Cited by 4 | Viewed by 4251

Abstract

We present preliminary results of the spectral analysis on the radial distributions of the star formation history in both a galaxy merger and a spiral isolated galaxy observed with MaNGA. We find that the central part of the isolated galaxy is composed by [...] Read more.

We present preliminary results of the spectral analysis on the radial distributions of the star formation history in both a galaxy merger and a spiral isolated galaxy observed with MaNGA. We find that the central part of the isolated galaxy is composed by older stellar population (~2 Gyr) than in the outskirts (~7 Gyr). Also, the time-scale is gradually larger from 1 Gyr in the inner part to 3 Gyr in the outer regions of the galaxy. In the case of the merger, the stellar population in the central region is older than in the tails, presenting a longer time-scale in comparison to central part in the isolated galaxy. Our results are in agreement with a scenario where spiral galaxies are built from inside-out. In the case of the merger, we find evidence that interactions enhance star formation in the central part of the galaxy. Full article

(This article belongs to the Special Issue 3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids)

► Show Figures

Figure 1

Journal Menu

Journal Browser

3D View on Interacting and Post-Interacting Galaxies from Clusters to Voids

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (11 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI