scholarly journals Composite bulges – II. Classical bulges and nuclear discs in barred galaxies: the contrasting cases of NGC 4608 and NGC 4643

2021 ◽  
Vol 502 (2) ◽  
pp. 2446-2473
Author(s):  
Peter Erwin ◽  
Anil Seth ◽  
Victor P Debattista ◽  
Marja Seidel ◽  
Kianusch Mehrgan ◽  
...  
Keyword(s):  
Large Scale ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Circular Structure ◽  
Model Predictions ◽  
The Galaxy ◽  
Central Regions ◽  
Total Light ◽  
Kinematic Analyses ◽  
Stellar Kinematic

ABSTRACT We present detailed morphological, photometric, and stellar-kinematic analyses of the central regions of two massive, early-type barred galaxies with nearly identical large-scale morphologies. Both have large, strong bars with prominent inner photometric excesses that we associate with boxy/peanut-shaped (B/P) bulges; the latter constitute ∼30 per cent of the galaxy light. Inside its B/P bulge, NGC 4608 has a compact, almost circular structure (half-light radius Re ≈ 310 pc, Sérsic n = 2.2) we identify as a classical bulge, amounting to 12.1 per cent of the total light, along with a nuclear star cluster (Re ∼ 4 pc). NGC 4643, in contrast, has a nuclear disc with an unusual broken-exponential surface-brightness profile (13.2 per cent of the light), and a very small spheroidal component (Re ≈ 35 pc, n = 1.6; 0.5 per cent of the light). IFU stellar kinematics support this picture, with NGC 4608’s classical bulge slowly rotating and dominated by high velocity dispersion, while NGC 4643’s nuclear disc shows a drop to lower dispersion, rapid rotation, V–h3 anticorrelation, and elevated h4. Both galaxies show at least some evidence for V–h3correlation in the bar (outside the respective classical bulge and nuclear disc), in agreement with model predictions. Standard two-component (bulge/disc) decompositions yield B/T ∼ 0.5–0.7 (and bulge n > 2) for both galaxies. This overestimates the true ‘spheroid’ components by factors of 4 (NGC 4608) and over 100 (NGC 4643), illustrating the perils of naive bulge-disc decompositions applied to massive barred galaxies.

scholarly journals Investigating the properties of a galaxy group at z = 0.6

2020 ◽  
Vol 15 (S359) ◽  
pp. 188-189
Author(s):  
Daniela Hiromi Okido ◽  
Cristina Furlanetto ◽  
Marina Trevisan ◽  
Mônica Tergolina
Keyword(s):  
Large Scale ◽  
The Other ◽  
Numerical Density ◽  
Spectroscopy Data ◽  
Stellar Kinematics ◽  
Galaxy Groups ◽  
The Galaxy ◽  
The Difference ◽  
The Impact ◽  
The Universe

AbstractGalaxy groups offer an important perspective on how the large-scale structure of the Universe has formed and evolved, being great laboratories to study the impact of the environment on the evolution of galaxies. We aim to investigate the properties of a galaxy group that is gravitationally lensing HELMS18, a submillimeter galaxy at z = 2.39. We obtained multi-object spectroscopy data using Gemini-GMOS to investigate the stellar kinematics of the central galaxies, determine its members and obtain the mass, radius and the numerical density profile of this group. Our final goal is to build a complete description of this galaxy group. In this work we present an analysis of its two central galaxies: one is an active galaxy with z = 0.59852 ± 0.00007, while the other is a passive galaxy with z = 0.6027 ± 0.0002. Furthermore, the difference between the redshifts obtained using emission and absorption lines indicates an outflow of gas with velocity v = 278.0 ± 34.3 km/s relative to the galaxy.

scholarly journals The Magnetized Disk-Halo Transition Region of M51

2018 ◽  
Vol 14 (A30) ◽  
pp. 319-322 ◽  
Author(s):  
M. Kierdorf ◽  
S. A. Mao ◽  
A. Fletcher ◽  
R. Beck ◽  
M. Haverkorn ◽  
...  
Keyword(s):  
Transition Region ◽  
Large Scale ◽  
Model Parameters ◽  
Very Large Array ◽  
X Band ◽  
Model Predictions ◽  
The Galaxy ◽  
Linearly Polarized ◽  
Grand Design ◽  
Different Depths

AbstractAn excellent laboratory for studying large scale magnetic fields is the grand design face-on spiral galaxy M51. Due to wavelength-dependent Faraday depolarization, linearly polarized synchrotron emission at different radio frequencies gives a picture of the galaxy at different depths: Observations at L-band (1 – 2 GHz) probe the halo region while at C- and X-band (4 – 8 GHz) the linearly polarized emission probe the disk region of M51. We present new observations of M51 using the Karl G. Jansky Very Large Array (VLA) at S-band (2 – 4 GHz), where previously no polarization observations existed, to shed new light on the transition region between the disk and the halo. We discuss a model of the depolarization of synchrotron radiation in a multilayer magneto-ionic medium and compare the model predictions to the multi-frequency polarization data of M51 between 1 – 8 GHz. The new S-band data are essential to distinguish between different models. Our study shows that the initial model parameters, i.e. the total regular and turbulent magnetic field strengths in the disk and halo of M51, need to be adjusted to successfully fit the models to the data.

scholarly journals Milky Way analogues in MaNGA: multiparameter homogeneity and comparison to the Milky Way

2019 ◽  
Vol 491 (3) ◽  
pp. 3672-3701 ◽  
Author(s):  
N Boardman ◽  
G Zasowski ◽  
A Seth ◽  
J Newman ◽  
B Andrews ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Milky Way ◽  
Central Star ◽  
Stellar Kinematics ◽  
Star Forming ◽  
Wide Range ◽  
The Galaxy ◽  
Central Regions ◽  
Galaxy Population ◽  
Stellar Masses

ABSTRACT The Milky Way provides an ideal laboratory to test our understanding of galaxy evolution, owing to our ability to observe our Galaxy over fine scales. However, connecting the Galaxy to the wider galaxy population remains difficult, due to the challenges posed by our internal perspective and to the different observational techniques employed. Here, we present a sample of galaxies identified as Milky Way analogues on the basis of their stellar masses and bulge-to-total ratios, observed as part of the Mapping Nearby Galaxies at Apache Point Observatory survey. We analyse the galaxies in terms of their stellar kinematics and populations as well as their ionized gas contents. We find our sample to contain generally young stellar populations in their outskirts. However, we find a wide range of stellar ages in their central regions, and we detect central active galactic nucleus-like or composite-like activity in roughly half of the sample galaxies, with the other half consisting of galaxies with central star-forming emission or emission consistent with old stars. We measure gradients in gas metallicity and stellar metallicity that are generally flatter in physical units than those measured for the Milky Way; however, we find far better agreement with the Milky Way when scaling gradients by galaxies’ disc scale lengths. From this, we argue much of the discrepancy in metallicity gradients to be due to the relative compactness of the Milky Way, with differences in observing perspective also likely to be a factor.

scholarly journals Observations of Galactic Magnetic Fields

2002 ◽  
Vol 12 ◽  
pp. 712-715 ◽  
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Density Wave ◽  
Upstream Region ◽  
Galactic Magnetic Fields ◽  
Barred Galaxies ◽  
Angular Momentum Transport ◽  
Central Regions ◽  
Spiral Structures ◽  
Field Lines

AbstractMagnetic fields are anchored in gas clouds. Field lines are tangled in spiral arms, but highly regularbetweenthe arms. The similarity of pitch angles between gaseous and magnetic arms suggests a coupling between the density wave and the magnetic wave. Observations of large-scale patterns in Faraday rotation favour a dynamo origin of the regular fields. Fields in barred galaxies do not reveal the strong shearing shocks observed in the cold gas, but swing smoothly from the upstream region into the bar. Magnetic fields are important for the dynamics of gas clouds, for the formation of spiral structures, bars and halos, and for mass and angular momentum transport in central regions.

scholarly journals Barred galaxies in cosmological zoom-in simulations: the importance of feedback

2019 ◽  
Vol 488 (2) ◽  
pp. 1864-1877 ◽  
Author(s):  
Tommaso Zana ◽  
Pedro R Capelo ◽  
Massimo Dotti ◽  
Lucio Mayer ◽  
Alessandro Lupi ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Stellar Content ◽  
Barred Galaxies ◽  
Stellar Feedback ◽  
The Galaxy ◽  
Key Factor ◽  
Formation And Evolution ◽  
Zoom In ◽  
Statistical Sample

Abstract Bars are a key factor in the long-term evolution of spiral galaxies, in their unique role in redistributing angular momentum and transporting gas and stars on large scales. The Eris-suite simulations are cosmological zoom-in, N-body, smoothed-particle hydrodynamic simulations built to follow the formation and evolution of a Milky-Way-sized galaxy across the build-up of the large-scale structure. Here we analyse and describe the outcome of two particular simulations taken from the Eris suite – ErisBH and Eris2k – which mainly differ in the prescriptions employed for gas cooling, star formation, and feedback from supernovae and black holes. Our study shows that the enhanced effective feedback in Eris2k, due to the collective effect of the different micro-physics implementations, results in a galaxy that is less massive than its ErisBH counterpart till z ∼ 1. However, when the stellar content is large enough so that global dynamical instabilities can be triggered, the galaxy in Eris2k develops a stronger and more extended bar with respect to ErisBH. We demonstrate that the structural properties and time evolution of the two bars are very different. Our results highlight the importance of accurate sub-grid prescriptions in cosmological zoom-in simulations of the process of galaxy formation and evolution, and the possible use of a statistical sample of barred galaxies to assess the strength of the stellar feedback.

scholarly journals Constraints on Bars in the Local Universe from 5000 SDSS Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 76-76 ◽  
Author(s):  
Fabio D. Barazza ◽  
Shardha Jogee ◽  
Irina Marinova
Keyword(s):  
Large Scale ◽  
Major Axis ◽  
Disk Galaxies ◽  
Semi Major Axis ◽  
Local Universe ◽  
Barred Galaxies ◽  
Sky Survey ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Local Disk

AbstractWe present the first study of bars in the local Universe, based on the Sloan Digitized Sky Survey (SDSS). The large sample of ~5000 local galaxies provides the largest study to date of local bars and minimizes the effect of cosmic variance. The sample galaxies have Mg ≤ −18.5 mag and cover the redshift range 0.01 ≤ z < 0.04. We use a color cut in the color-magnitude diagram and the Sérsic index n to identify disk galaxies. We characterize bars and disks using r-band images and the method of iterative ellipse fits and quantitative criteria developed in Jogee at al. (2004, ApJL, 615, L105). After excluding highly inclined (i>60°) systems our results are: (1) the optical (r-band) fraction of barred galaxies among local disk galaxies is 43% (Figure 1, left panel), which confirms the ubiquity of local bars, in agreement with other optical studies based on smaller samples (e.g. Eskridge et al 2000, AJ, 119, 536, Marinova & Jogee 2006, astro-ph/0608039); (2) the optical bar fraction rises for bluer galaxies, suggesting a relation between bars and star formation (Figure 1, middle panel); (3) preliminary analyzes suggest that the optical bar fraction increases steeply with the galaxy effective radius (reff, Figure 1, right panel); (4) the optical bar fraction at z ~ 0 is ~35% for bright disks (Mg ≤ −19.3 mag) and strong (bar ellipticity >0.4), large-scale (bar semi-major axis >1.5 kpc) bars, which is comparable to the value of ~30 ± 6% reported earlier (Jogee et al 2004) for similar disks and bars at z ~ 0.2 − 1.0.

scholarly journals Morphology, Stellar Kinematics and Dynamics of Barred Galaxies

1983 ◽  
Vol 100 ◽  
pp. 193-196
Author(s):  
John Kormendy
Keyword(s):  
Velocity Dispersion ◽  
Rotation Velocity ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Circular Velocity ◽  
Local Ratio ◽  
The Galaxy ◽  
Stellar Velocity ◽  
Random Motions ◽  
Velocity Dispersions

A brief review is given of the morphology of barred galaxies, following Kormendy (1981, 1982). The features illustrated include bulges, bars, disks, lenses, and inner and outer rings.Most of the paper is devoted to a detailed discussion of the absorption-line velocity field of the prototypical SBO galaxy NGC 936. The stars in the bar region show systematic non-circular streaming motions, with average orbits which are elongated parallel to the bar. Beyond the end of the bar, the data are consistent with circular orbits. The bar region also shows large random motions: the velocity dispersion at one-half of the radius of the bar is 1/2–2/3 as large as the maximum circular velocity. The observed kinematics are qualitatively and quantitatively similar to the behavior of n-body models by Miller and Smith (1979) and by Hohl and Zang (1979). The galaxy and the models show similar radial dependences of simple dimensionless parameters that characterize the dynamics. These include the local ratio of rotation velocity to velocity dispersion, which measures the relative importance of the ordered and random motions discussed above. Also similar are the residual streaming motions (relative to the circular velocity) in a frame of reference rotating with the bar. Circulation is in the same direction as rotation in all galaxies studied to date. Thus, except for the fact that NGC 936 has a slightly larger velocity dispersion, both n-body models are good first-order approximations to bars. Thus bars are different from elliptical galaxies, which in general are also triaxial, but which rotate slowly. This study of NGC 936 will be published in Kormendy (1983).A brief discussion is given of the kinematics of lens components. In both barred and unbarred galaxies, the velocity dispersions in the inner parts of lenses are large. The ratio of rotational to random kinetic energy is ∼ 1/2 at 1/3–1/2 of the radius of the lens. This ratio then decreases to small values at the rim of the lens. Thus at least some kinds of disk components have large stellar velocity dispersions, even in unbarred galaxies.

scholarly journals Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

2020 ◽  
Vol 494 (4) ◽  
pp. 5936-5960 ◽  
Author(s):  
F Fragkoudi ◽  
R J J Grand ◽  
R Pakmor ◽  
G Blázquez-Calero ◽  
I Gargiulo ◽  
...  
Keyword(s):  
Milky Way ◽  
Stellar Populations ◽  
Ex Situ ◽  
Mass Ratio ◽  
Star Forming ◽  
Barred Galaxies ◽  
The Galaxy ◽  
Central Regions ◽  
Major Merger

ABSTRACT We explore the chemodynamical properties of a sample of barred galaxies in the Auriga magnetohydrodynamical cosmological zoom-in simulations, which form boxy/peanut (b/p) bulges, and compare these to the Milky Way (MW). We show that the Auriga galaxies which best reproduce the chemodynamical properties of stellar populations in the MW bulge have quiescent merger histories since redshift z ∼ 3.5: their last major merger occurs at $t_{\rm lookback}\gt 12\, \rm Gyr$, while subsequent mergers have a stellar mass ratio of ≤1:20, suggesting an upper limit of a few per cent for the mass ratio of the recently proposed Gaia Sausage/Enceladus merger. These Auriga MW-analogues have a negligible fraction of ex-situ stars in the b/p region ($\lt 1{{\ \rm per\ cent}}$), with flattened, thick disc-like metal-poor stellar populations. The average fraction of ex-situ stars in the central regions of all Auriga galaxies with b/p’s is 3 per cent – significantly lower than in those which do not host a b/p or a bar. While the central regions of these barred galaxies contain the oldest populations, they also have stars younger than 5 Gyr (&gt;30 per cent) and exhibit X-shaped age and abundance distributions. Examining the discs in our sample, we find that in some cases a star-forming ring forms around the bar, which alters the metallicity of the inner regions of the galaxy. Further out in the disc, bar-induced resonances lead to metal-rich ridges in the Vϕ − r plane – the longest of which is due to the Outer Lindblad Resonance. Our results suggest the Milky Way has an uncommonly quiet merger history, which leads to an essentially in-situ bulge, and highlight the significant effects the bar can have on the surrounding disc.

scholarly journals Morphological transformation of NGC 205?

2009 ◽  
Vol 5 (S262) ◽  
pp. 426-427
Author(s):  
Ivo Saviane ◽  
Lorenzo Monaco ◽  
Tony Hallas
Keyword(s):  
Globular Clusters ◽  
Large Scale ◽  
Central Field ◽  
Morphological Transformation ◽  
The Galaxy ◽  
Central Regions ◽  
Radial Orbit ◽  
Specific Frequency ◽  
Stellar Associations ◽  
First Time

NGC 205 is a small galaxy (M/M⊙ = 0.7 × 109; MV = −16.6) currently located 36′ NW of M31. It is classified as dE because in ground-based images it appears as an elliptical body. However past investigations have revealed characteristics that are more typical of a disk galaxy: the specific frequency of globular clusters is 1.8; the large scale dynamics shows partial rotational support; there is a significant amount (106M⊙) of rotating gas (molecular and atomic) and dust; the central regions harbor a fairly complex stellar population, including a 100–500 Myr old nucleus surrounded by 50- and 100-Myr old stellar associations (see references in Monaco et al. 2009; M09). Very recently, thanks to hst/acs imaging we have been able to reveal a young central ‘field’ population (M09), extending out to ~40″ in radius (~160 pc). The luminosity function of the main sequence can be fitted with Saviane et al. (2004) model of continuous star formation (SF) from at least ~600 Myr ago to ~60 Myr ago. We found that 1.5 × 105M⊙ in stars were produced from ~300 Myr to ~60 Myr ago, with a SF rate of 7 × 10−4M⊙ yr−1. A continuous SF seems to support the latest simulations of NGC 205 orbit: Howley et al. (2008) found that the galaxy must be moving with a velocity 300–500 km s−1 (comparable to the escape velocity) along an almost radial orbit, and it should be approaching M31 for the first time. An episodic SF triggered by passages through M31 disk every ~300 Myr in a bound orbit (Cepa & Beckman 1988) is excluded by our data.

Active galaxies and radiative heating

2005 ◽  
Vol 363 (1828) ◽  
pp. 667-683 ◽  
Author(s):  
Jeremiah P. Ostriker ◽  
Luca Ciotti
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Large Scale ◽  
Thermal State ◽  
Rest Mass ◽  
Radiant Energy ◽  
Radiative Heating ◽  
Massive Black Hole ◽  
The Galaxy ◽  
Central Regions

There is abundant evidence that heating processes in the central regions of elliptical galaxies have both prevented large–scale cooling flows and assisted in the expulsion of metal rich gas. We now know that each such spheroidal system harbours in its core a massive black hole weighing ca. 0.13% of the mass in stars and also know that energy was emitted by each of these black holes with an efficiency exceeding 10% of its rest mass. Since, if only 0.5% of that radiant energy were intercepted by the ambient gas, its thermal state would be drastically altered, it is worth examining in detail the interaction between the out–flowing radiation and the equilibrium or inflowing gas. On the basis of detailed hydrodynamic computations we find that relaxation oscillations are to be expected with the radiative feedback quite capable of regulating both the growth of the central black hole and also the density and thermal state of the gas in the galaxy. Mechanical input of energy by jets may assist or dominate over these radiative effects. We propose specific observational tests to identify systems which have experienced strong bursts of radiative heating from their central black holes.

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