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 (>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 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 Reconstructing the Last Major Merger of the Milky Way with the H3 Survey

2021 ◽  
Vol 923 (1) ◽  
pp. 92
Author(s):  
Rohan P. Naidu ◽  
Charlie Conroy ◽  
Ana Bonaca ◽  
Dennis Zaritsky ◽  
Rainer Weinberger ◽  
...  
Keyword(s):  
Milky Way ◽  
Age Distribution ◽  
Major Axis ◽  
Angular Momenta ◽  
Outer Disk ◽  
The Galaxy ◽  
Stellar Halo ◽  
Major Merger ◽  
Triaxial Shape

Abstract Several lines of evidence suggest that the Milky Way underwent a major merger at z ∼ 2 with the Gaia-Sausage-Enceladus (GSE) galaxy. Here we use H3 Survey data to argue that GSE entered the Galaxy on a retrograde orbit based on a population of highly retrograde stars with chemistry similar to the largely radial GSE debris. We present the first tailored N-body simulations of the merger. From a grid of ≈500 simulations we find that a GSE with M ⋆ = 5 × 108 M ⊙, M DM = 2 × 1011 M ⊙ best matches the H3 data. This simulation shows that the retrograde stars are stripped from GSE’s outer disk early in the merger. Despite being selected purely on angular momenta and radial distributions, this simulation reproduces and explains the following phenomena: (i) the triaxial shape of the inner halo, whose major axis is at ≈35° to the plane and connects GSE’s apocenters; (ii) the Hercules-Aquila Cloud and the Virgo Overdensity, which arise due to apocenter pileup; and (iii) the 2 Gyr lag between the quenching of GSE and the truncation of the age distribution of the in situ halo, which tracks the lag between the first and final GSE pericenters. We make the following predictions: (i) the inner halo has a “double-break” density profile with breaks at both ≈15–18 kpc and 30 kpc, coincident with the GSE apocenters; and (ii) the outer halo has retrograde streams awaiting discovery at >30 kpc that contain ≈10% of GSE’s stars. The retrograde (radial) GSE debris originates from its outer (inner) disk—exploiting this trend, we reconstruct the stellar metallicity gradient of GSE (−0.04 ± 0.01 dex r 50 − 1 ). These simulations imply that GSE delivered ≈20% of the Milky Way’s present-day dark matter and ≈50% of its stellar halo.

scholarly journals A sub-kiloparsec-scale view of un-lensed submillimeter galaxies

2019 ◽  
Vol 15 (S352) ◽  
pp. 287-290
Author(s):  
Ken-ichi Tadaki ◽  
Daisuke Iono
Keyword(s):  
Surface Density ◽  
Gravitational Instability ◽  
Effective Radius ◽  
The Other ◽  
Ex Situ ◽  
Submillimeter Galaxies ◽  
The Galaxy ◽  
Central Regions ◽  
Kinematic Properties

AbstractSubmillimeter galaxies at z > 3 building up their central cores through compact starbursts with an effective radius of 1–2 kpc. Our ALMA high-resolution observations reveal off-center gas clumps in a submillimeter galaxy at z = 4.3, COSMOS-AzTEC-1, as well as a rotation-dominated disk. Exploiting the kinematic properties and the spatial distribution of gas mass surface density, we find that the starburst disk is gravitationally unstable. This result is consistent with a scenario where in-situ clumps are formed through disk instability. On the other hand, we find evidence for an ex-situ clump that does not corotate with the starburst disk. The accretion of such a non-corotating clump could stimulate violent disk instability, driving gas inflows into the central regions of the galaxy. Our results suggest that compact cores are formed through an extreme starburst due to a gravitational instability, triggered by non-corotating clumps.

scholarly journals A contribution of star-forming clumps and accreting satellites to the mass assembly of z ∼ 2 galaxies

2019 ◽  
Vol 489 (2) ◽  
pp. 2792-2818 ◽  
Author(s):  
A Zanella ◽  
E Le Floc’h ◽  
C M Harrison ◽  
E Daddi ◽  
E Bernhard ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Ratio ◽  
Star Forming ◽  
Spatially Resolved ◽  
The Galaxy ◽  
Mass Assembly

ABSTRACT We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M⋆ ≳ 109 M⊙) have lifetimes of ∼650 Myr, and the less massive ones (108 < M⋆ < 109 M⊙) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.

scholarly journals VINTERGATAN III: how to reset the metallicity of the Milky Way

2021 ◽  
Vol 503 (4) ◽  
pp. 5868-5876
Author(s):  
Florent Renaud ◽  
Oscar Agertz ◽  
Eric P Andersson ◽  
Justin I Read ◽  
Nils Ryde ◽  
...  
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Plane ◽  
First Stars ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Chemical Content ◽  
Major Merger ◽  
Purely Sequential

ABSTRACT Using the cosmological zoom simulation VINTERGATAN, we present a new scenario for the onset of star formation at the metal-poor end of the low-[α/Fe] sequence in a Milky Way-like galaxy. In this scenario, the galaxy is fuelled by two distinct gas flows. One is enriched by outflows from massive galaxies, but not the other. While the former feeds the inner galactic region, the latter fuels an outer gas disc, inclined with respect to the main galactic plane, and with a significantly poorer chemical content. The first passage of the last major merger galaxy triggers tidal compression in the outer disc, which increases the gas density and eventually leads to star formation, at a metallicity 0.75 dex lower than the inner galaxy. This forms the first stars of the low-[α/Fe] sequence. These in situ stars have halo-like kinematics, similar to what is observed in the Milky Way, due to the inclination of the outer disc that eventually aligns with the inner one via gravitational torques. We show that this tilting disc scenario is likely to be common in Milky Way-like galaxies. This process implies that the low-[α/Fe] sequence is populated in situ, simultaneously from two formation channels, in the inner and the outer galaxy, with distinct metallicities. This contrasts with purely sequential scenarios for the assembly of the Milky Way disc and could be tested observationally.

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 &gt; 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 A galaxy’s accretion history unveiled from its integrated spectrum

2019 ◽  
Author(s):  
Alina Boecker ◽  
Ryan Leaman ◽  
Glenn van de Ven ◽  
Mark A Norris ◽  
J Ted Mackereth ◽  
...  
Keyword(s):  
Stellar Populations ◽  
Mass Function ◽  
Stellar Mass ◽  
Ex Situ ◽  
Future Application ◽  
Chemical Enrichment ◽  
Spectral Fitting ◽  
Regularization Techniques ◽  
Galaxy Masses

Abstract We present a new method of quantifying a galaxy’s accretion history from its integrated spectrum alone. Using full spectral fitting and calibrated regularization techniques we show how we can accurately derive a galaxy’s mass distribution in age-metallicity space and further separate this into stellar populations from different chemical enrichment histories. By exploiting the fact that accreted lower mass galaxies will exhibit an offset to lower metallicities at fixed age compared to the in-situ stellar population, we quantify the fraction of light that comes from past merger events, that are long since mixed in phase-space and otherwise indistinguishable. Empirical age-metallicity relations (AMRs) parameterized for different galaxy masses are used to identify the accreted stellar populations and link them back to the progenitor galaxy’s stellar mass. This allows us to not only measure the host galaxy’s total ex-situ mass fraction (facc), but also quantify the relative amount of accreted material deposited by satellite galaxies of different masses, i.e. the accreted satellite mass function in analogy to the subhalo mass function. Using mock spectra of present-day, early-type galaxies with total stellar mass ∼109 − 1012 M⊙ from the EAGLE simulation suite we demonstrate that our method can recover the total accreted fraction to within $\approx 38 \%$, the stellar mass of the most massive accreted subhalo to within $\approx 56 \%$ and the slope of the accreted satellite mass function to within $\approx 17 \%$ of the true values from the EAGLE merger trees. Future application of this method to observations could potentially provide us accretion histories of hundreds of individual galaxies, for which deep integrated light spectroscopy is available.

scholarly journals Predicting accreted satellite galaxy masses and accretion redshifts based on globular cluster orbits in the E-MOSAICS simulations

2020 ◽  
Vol 499 (4) ◽  
pp. 4863-4875
Author(s):  
Joel L Pfeffer ◽  
Sebastian Trujillo-Gomez ◽  
J M D Kruijssen ◽  
Robert A Crain ◽  
Meghan E Hughes ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Star Cluster ◽  
Low Energy ◽  
Orbital Energy ◽  
High Energies ◽  
Satellite Galaxy ◽  
The Galaxy ◽  
Galaxy Masses

ABSTRACT The ages and metallicities of globular clusters (GCs) are known to be powerful tracers of the properties of their progenitor galaxies, enabling their use in determining the merger histories of galaxies. However, while useful in separating GCs into individual accretion events, the orbits of GC groups themselves have received less attention as probes of their progenitor galaxy properties. In this work, we use simulations of galaxies and their GC systems from the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE project to explore how the present-day orbital properties of GCs are related to the properties of their progenitor galaxies. We find that the orbits of GCs deposited by accretion events are sensitive to the mass and merger redshift of the satellite galaxy. Earlier mergers and larger galaxy masses deposit GCs at smaller median apocentres and lower total orbital energy. The orbital properties of accreted groups of GCs can therefore be used to infer the properties of their progenitor galaxy, though there exists a degeneracy between galaxy mass and accretion time. Combining GC orbits with other tracers (GC ages, metallicities) will help to break the galaxy mass/accretion time degeneracy, enabling stronger constraints on the properties of their progenitor galaxy. In situ GCs generally orbit at lower energies (small apocentres) than accreted GCs, however they exhibit a large tail to high energies and even retrograde orbits (relative to the present-day disc), showing significant overlap with accreted GCs. Applying the results to Milky Way GCs groups suggests a merger redshift z ∼ 1.5 for the Gaia Sausage/Enceladus and z &gt; 2 for the ‘low-energy’/Kraken group, adding further evidence that the Milky Way had two significant mergers in its past.

Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66

2018 ◽  
Vol 14 (S344) ◽  
pp. 420-421
Author(s):  
M. E. Sharina ◽  
L. N. Makarova ◽  
D. I. Makarov
Keyword(s):  
Surface Density ◽  
Globular Clusters ◽  
Stellar Populations ◽  
Density Profiles ◽  
Dwarf Spheroidal Galaxies ◽  
Star Forming ◽  
Central Regions ◽  
Low Metallicity ◽  
High Metallicity ◽  
Spheroidal Galaxies

AbstractWe compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.

scholarly journals The vertical metallicity gradients of mono-age stellar populations in the Milky Way thin disk

2017 ◽  
Vol 13 (S334) ◽  
pp. 281-282
Author(s):  
Ioana Ciucă ◽  
Daisuke Kawata ◽  
Jane Lin ◽  
Luca Casagrande ◽  
George Seabroke ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Stellar Populations ◽  
Thin Disk ◽  
Dwarf Stars ◽  
Star Forming ◽  
Data Release ◽  
The Cross

AbstractWe investigate the vertical metallicity gradients of five mono-age stellar populations between 0 and 11 Gyr for a sample of 18 435 dwarf stars selected from the cross-matched Tycho-Gaia Astrometric Solution (TGAS) and RAdial Velocity Experiment (RAVE) Data Release 5. We find a correlation between the vertical metallicity gradients and age, with no vertical metallicity gradient in the youngest population and an increasingly steeper negative vertical metallicity gradient for the older stellar populations. We also find that the intrinsic dispersion in metallicity increases steadily with age. Our results are consistent with a scenario that thin disk stars formed from a flaring thin star-forming disk.

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